Endocrinology and Metabolism

Seung Joon Park (Park SJ)

9 Articles

Changes in Somatostatin Receptor mRNA Levels by G Protein Mutation in GH3 Cells Which Show Responsiveness to Growth Hormone-Releasing Hormone.: Eun Hee Kim, Sook Jin Sohn, Min A Lee, Sang Hee Seo, Sung Hee Ju, Dahm Lee, Hyun Ju Chung, Jee Chang Jung, Seung Joon Park; J Korean Endocr Soc. 2005;20(4):323-333. Published online August 1, 2005; DOI: https://doi.org/10.3803/jkes.2005.20.4.323

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Abstract PDF: BACKGROUND
S: GH3 cells lack growth hormone(GH)-releasing hormone(GHRH) receptors. In this study, GH3 cells permanently transfected with human GHRH receptor cDNA(GH3-GHRHR cells), were established in order to examine the effects of GHRH and G protein mutation(gsp oncogene) on the levels of somatostatin receptor mRNA. METHODS: GH3 cells were permanently transfected with a plasmid expressing human GHRH receptor cDNA. The GHRH receptor mRNA was detected by RT-PCR. The responsiveness to GHRH was evaluated using a GHRH binding assay, Western blot analysis, Northern blot analysis, and measurements of the intracellular cAMP levels and GH release. Cells were transiently transfected with the gsp oncogene, and then treated with GHRH or octreotide for 4h. The sst1 and sst2 mRNA levels were measured using real-time RT-PCR analyses. RESULTS: GHRH receptor mRNA was detected in the GH3 cells permanently transfected with human GHRH receptor cDNA. The GHRH binding assay showed that GHRH was bound to the GH3-GHRHR cells. The GHRH treatment increased the intracellular cAMP levels, GH release, GH mRNA levels, and MAPK activity, as well as the levels of sst1 and sst2 mRNA. Transient expression of the gsp oncogene for 48h increased the cAMP, GH release, and levels of sst1 and sst2 mRNA. In the gsp-transfected GH3-GHRHR cells, GHRH stimulation resulted in decreases in the magnitude of the increase in the levels of sst1 and sst2 mRNA compared to those transfected with a control vector. Octreotide treatment did not alter the levels of sst1 and sst2 mRNA in either the control or gsp-transfected cells. CONCLUSION: These results suggest that GH3 cells permanently transfected with the GHRH receptor are useful in the in vitro studies on the actions of GHRH. The gsp oncogene was shown to increases the levels of sst1 and sst2 mRNA in GH3 cells, but these findings are unlikely to be the major mechanism by which gsp-positive pituitary tumors show a greater response to somatostatin. The discrepancy between the in vivo and these in vitro results should be examined further.

Gene Expression of the Somatostatin Receptors, Gi2 alpha and Pit-1 alpha in GH3 Cells Permanently Transfected with a Mutant Gs alpha Gene.: Cheol young Park, In myung Yang, Eun hee Kim, Sook jin Sohn, Mee sook Ryu, Jeong taek Woo, Sung woon Kim, Jin woo Kim, Young seol Kim, Young kil Choi, Seung joon Park; J Korean Endocr Soc. 2002;17(2):170-182. Published online April 1, 2002

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Abstract PDF: BACKGROUND
Cyclic AMP stimulates the expression of the somatostatin (SRIF) receptor (sst1-5) and human growth hormone (GH)-secreting pituitary tumors with the gsp oncogene which increases intracellular cAMP levels, and shows a good inhibitory response of the GH to SRIF. Taken together, we hypothesized that the gsp oncogene may increase the SRIF receptor expression or and factors related to the postreceptor signal transduction of the SRIF, in order to enhance its responsiveness to SRIF. To test this hypothesis, we investigated if the gsp oncogene could increase the sst1, sst2, Gi2 alpha, and pit-1 alpha gene expression in GH3 cells. METHODS: GH3 cells were permanently transfected with the plasmid expressing Gs alpha gene, where the arginine of codon 201 was replaced with histidine. Intracellular cAMP levels and GH concentrations were measured by radioimmunoassays. Gene expressions of the sst1, sst2, Gi2 alpha, and pit-1 alpha were determined by RT-PCR. RESULTS: Intracellular cAMP levels and medium GH release were increased by 1.7 and 2.7-fold in GH3 cells expressing the gsp oncogene, respectively. In GH3 cells expressing the gsp oncogene, the sst1 mRNA levels were decreased, whereas those of the sst2, Gi2 alpha and pit-1 alpha mRNA were increased. A 4-h forskolin (10 M) stimulation remarkably increased the sst1 and sst2 mRNA levels in GH3 cells expressing wild and mutant Gs alpha . However, forskolin did not affect the Gi2 alpha and pit-1 alpha mRNA levels. In contrast, SRIF (1 M, 2 h) decreased the sst2 mRNA levels only in GH3 cells expressing the gsp oncogene. CONCLUSION: These results suggest that higher expressions of sst2, Gi2 alpha, and pit-1 alpha, induced by the gsp oncogene may be a mechanism by which gsp-positive pituitary tumors show a greater response to SRIF. The discrepancy between these and in vivo results should be explored further.

Gene Expression of Somatostatin Receptor (Subtype 2 & 5), Gi2 alpha and Pit-1 in GH-secreting Pituitary Adenomas.: Mee sook Ryu, In myung Yang, Cheol young Park, Jeong taek Woo, Sung woon Kim, Jin Woo Kim, Young seoul Kim, Young kil Choi, En hee Kim, Seung joon Park, Kook gi Kim; J Korean Endocr Soc. 2002;17(2):158-169. Published online April 1, 2002

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Abstract PDF: BACKGROUND
Mutation of Gs protein subunit (gsp oncogene), detected in about 30~40% of growth hormone (GH)-secreting pituitary tumors, is associated with an increased long-acting somatostatin analog octreotide sensitivity. However, the mRNA expression of somatostatin receptor (sst) was not changed in the GH-secreting pituitary tumor, regardless of whether they were gsp oncogene positive or negative. This suggests that the expression of genes coding for Gi2 alpha , Pit-1 and the other factors involved in the regulation of secretory activity in somatotrophs is likely to be altered in gsp oncogene positive tumors. We observed the impact of the gsp oncogene on the expression of the genes coding for Gi2 alpha, Pit-1 and sst (2&5) in GH-secreting pituitary tumors. METHODS: The GH response to octreotide was examined in 13 acromegalic patients before transsphenoidal adenomectomy. Genomic DNA and RNA were extracted from fresh frozen tumor tissues. PCR was performed to amplify and sequence the region between codon 184 and 251 that includes exons 8 and 9 of the Gs gene. Sst2, sst5, Gi2 alpha and Pit-1 mRNA levels were measured by semi-quantitative RT-PCR. RESULTS: Sst2 and sst5 mRNA transcripts were detected in all tumors (7 gsp +, 6 gsp-). The amount of sst transcripts varied considerably varied between the tumors. There were no significant differences in sex, age, tumor size, grade or basal GH levels. Pit-1 and sst2 mRNA levels were not different. In contrast, Gi2 alpha mRNA levels were significantly higher in gsp (+) while sst5 mRNA levels were higher in gsp (-). CONCLUSION: These data suggests that gsp oncogene may increase Gi2 alpha levels but decrease sst5 mRNA levels. However, Pit-1 and sst2 mRNA expression may not be affected by gsp oncogene. The increased expression of the Gi2 alpha gene might be an inhibitory compensatory response to the action of gsp oncogene.

Thyrotropin-releasing Hormone(TRH) Receptor Gene Expression in GH3 Cells Permanently Transfected with a Mutant Gs alpha Gene.: Seung Joon Park, In Myung Yang, Sung Vin Yim, Joo Ho Chung, Jee Chang Jung, Kye Chang Ko, Young Seol Kim, Young Kil Choi; J Korean Endocr Soc. 2000;15(1):46-54. Published online January 1, 2001

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Abstract PDF: BACKGROUND
Gs alpha gene mutation, that constitutively increases intracellular cAMP, is found in some acromegalic patients. It was demonstrated that increased intracellular cAMP levels suppress the expression of rat TRH receptor (TRH-R) mRNA. We previously demonstrated that transient expression of a mutant Gs alpha gene suppress the rat TRH-R gene expression in the cultured rat growth hormone-secreting tumor cell line (GH3), whereas TRH-R gene expression in adenomas with Gs alpha gene mutation (gsp oncogene) did not differ from that in tumors without the mutation. The discrepancy suggests the possibilities that the effect of permanent expression of mutant Gs alpha gene on TRH-R gene expression is different from that of transient expression of the mutant gene and hypothalamic hormones including TRH regulate the gene expression. METHODS: We investigated whether permanent expression of the mutant-type Gs alpha does not suppress the TRH receptor gene expression in GH3 cells, and whether TRH suppresses the gene expression by using reverse transcription-polymerase chain reaction (RT-PCR) and in vitro transcription. RESULTS: Permanent expression of a mutant-type Gs alpha increased basal cAMP levels up to 1.7-fold relative to the controls, whereas the wild-type cell line did not show increased cAMP levels. Permanent expression of a mutant-type Gs alpha increased TRH receptor mRNA level up to 2.8 fold compared with the controls. Treatment of the permanently transfected GH3 cells with TRH suppressed TRH-R gene expression more prominently compared to the wild type GH3 cells. CONCLUSION: These results suggest that permanent expression of mutant Gs alpha enhances the expression of TRH-R in GH-secreting pituitary tumors with gsp oncogene, but the gene expression may also be regulated by other factors including TRH.

Relationship between the Expression of Growth Hormone-Releasing Hormone Receptor Gene and Endocrinologic Profiles in GH-Secreting Pituitary Adenomas.: Sung Woon Kim, Jin Woo Kim, Young Seol Kim, Young Kil Choi, Seung Joon Park, In Myoung Yang, Jung Taek Woo, Mi Sook Ryu, Chul Young Park, Sun Woo Kim; J Korean Endocr Soc. 1999;14(2):241-254. Published online January 1, 2001

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Abstract PDF: BACKGROUND
Growth hormone-releasing hormone (GHRH) plays a key role in the regulation of the proliferation and differentiation of somatomammotroph cells as well as secretion of GH. The actions of GHRH are mediated through the GHRH receptor (GHRH-R) that is a G protein coupled receptor with seven transmembrane domains. It has been demonstrated that alternative splicing occurs in the third cytoplasmic domain of rat and human GHRH-R mRNA, However, the clinical significance of the altemative splicing remains to be unsolved. To find an insight into the clinical significance, we investigate the correlation between the GHRH-R gene expression and a variety of clinical clinical and endocrinological findings in 11 acromegalic patients. METHODS: Eleven acromegalic patients (3 males and 8 females, mean age 43.5 years) were included in this study. Six endocrine tests were carried out to evaluate the GH seeretory function of tumors. Invasiveness of tumors were evaluated by preoperative MRI findings on the basis of Hardys classification. Sequence the gsp oncogene and estimate the GHRH-R gene expression by RT-PCR and in vitro transcription. RESULTS: Three different sized cDNA fragments, 250 bp, 700 bp and 810 bp, were found after RT-PCR. The amount of 250 bp fragment was higher than those of the other two fragments. The clinical findings (age, size, GH level, frequency of paradoxical response to TRH or GnRH, octreotide response, hypothalamic somatostatinergic activity) of the group with high expression of the 250 bp fragment did not significantly differ from those of the group with low expression. The GHRH-R gene expression of tumors with gsp oncogene did not significantly differ from that of tumors without gsp oncogene. CONCLUSION: These results suggest that the expression of GHRH-R gene may not be an important determinant for tumor growth, and the lower GH response to GHRH of tumors with gsp oncogene may not be attributed to the lower expression of GHRH-R gene. The expression of GHRH-R is likely to be regulated by a certain property of tumors for GH secretion and growth.

Gene Expression of Somatostatin Receptor Subtype 2 and 5 in GH-Secreting Pituitary Adenomas.: Sung Woon Kim, Jin Woo Kim, Young Seol Kim, Young Kil Choi, Seung Joon Park, In Myoung Yang, Jung Taek Woo, Kook Ki Kim; J Korean Endocr Soc. 1997;12(4):508-517. Published online January 1, 2001

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SSTR2 and SSTR5 are most frequently observed in GH-secreting pituitary tumors, and SSTR5 is believed to be more specific to mammosomatotroph lineage. Octreotide binds with high affinity to those two types. There is no report that investigates the quantitative comparison of the two subtype gene expressions, and the correlation between their gene expressions and GH response to octreotide in GH-secreting pituitary adenomas. METHOD: GH response to octreotide was examined in 8 acromegalic patients before transsphenoidal adenomectomy. Genomic DNA and RNA were prepared from fresh frozen tumor tissues. PCR was performed to amplify and sequence the region between codon 184 and 251 that includes exons 8 and 9 of the Gas gene. mRNAs of SSTR2 and SSTRS were quantitated by the comparative RT-PCR and in vitro transcription. RESULTS: The in vitro transcripts of SSTR2 and SSTR5 cDNA were detected in all tumors. The amount of SSTR transcripts was considerably variable between the tumors. The amount of SSTR5 transcript was significantly smaller than that of SSTR2 transcript (0.07+-0.02 vs. 0.87+-0.10), and they did not show any correlation . There was no signicant difference in sex, age, tumor size and grade, basal GH levels, and the GH responses to octreotide between the group with high and low SSTR gene expression. No significant correlation was found between the GH response to octreotide and the amount of SSTR2 transcript, wherease the amount of SSTR5 transcripts showed a tendency of negative correlation with the octreotide response. Tumors with gsp oncogene showed significantly higher response to octreotide than those without the oncogene. The amount of SSTRS transcript in gsp-positive tumors was significantly smaller than in gsp-negative tumors (0.03+-0.01 vs. 0.12+-0.03). CONCLUSION: These results suggest that SSTRS gene expression is lower than that of SSTR2 in GH-secreting adenomas. It is probably attributed to the binding of somatostatin to SSTR5 which has a higher affinity to the hypothalamic somatostatin, Tumors with gsp-oncogene is likely to express a higher density of SSTR5 than those without the oncogene.

Effect of Ga2 gene mutation on the Expression of Thyrotropin-Releasing Hormone ( TRH ) Receptor Gene in GH3 Cells.: Seung Joon Park, In Myung Yang, Jeong Hwa Ryu, Joo Ho Chung, Jee Chang Jung, Kye Chang Ko, Young Seol Kim, Young Kil Choi; J Korean Endocr Soc. 1997;12(3):357-363. Published online January 1, 2001

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Expression of TRH Receptor Gene in GH-Secreting Piruitary Adenomas.: In Myung Yang, Seung Joon Park, Jeong Wha Ryu, Joo Ho Chung, Mee Sook Ryu, Jeong Taek Woo, Sung Woon Kim, Jin Woo Kim, Young Seol Kim, Young Kil Choi; J Korean Endocr Soc. 1997;12(3):349-356. Published online January 1, 2001

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Abstract PDF: Background
To test the hypothesis that Galphas gene mutation may suppress the expression of TRH-R gene, we investigated whether hTRH-R gene expression is lower in human GH-secreting pituitary adenomas with Galphas mutation than in tumors without the mutation. Method: TRH-induced paradoxical response of GH was observed in 8 acromegalic patients. The mutation of gene was identified by direct sequencing of the genomic DNA prepared from GH-secreting pituitary adenomas. The expression of hTRHT mRNA was quantitated by RT-PCR. Results: The transcript of hTRH-R gene was detected in 6 of 8(75%) tumors. Three of these(50%) showed the paradoxical GH response to TRH and the other three patients did not show the response. The relative expression of hTRH-R mRNA in the tumors from patients with the paradoxical response of GH to TRH did not differ from that in the tumors from patients without the paradoxical response. Direct PCR sequencing of Galphas disclosed a mutant allele and a normal allele only at codon 201 in 4 of 8 tumors. The paradoxical response to TRH was observed in 2 of 4 patients without the mutation, and 2 of 4 patients with the mutation. The hTRH-R gene expression of pituitary adenomas did not differ between the tumors without the mutation and those with mutation. Conclusion: This study suggests that the expression of TRH-R gene is not likely to be a main determinant for the paradoxical response of GH to TRH, and that Galphas mutation does not seem to suppress the gene expression of TRH-R in GH secreting adenoma.

Identification of TPA - Response Element (TRE) in the Rat Thyrotropin - Releasing Hormone (TRH) Gene.: Woon Won Jung, Young Kil Choi, In Myung Yang, Kwang Sik Seo, Jeong Taek Woo, Sung Woon Kim, Jin Woo Kim, Young Seol Kim, Young Kil Choi, Seung Joon Park; J Korean Endocr Soc. 1994;10(3):200-213. Published online November 6, 2019

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Abstract PDF: There are two potential imperfect copies of the TRE consensus sequence between -47 and -113bp position on 5' upstream of the rat TRH gene. The upstream element(5'-TGcCgTCA-3') is located between -101 bp and -94 bp, and the downstream element(5'-TGAcCTCA-3') is positioned between -59bp and -52bp relative to the stranscription start site. The downstream variant differs from the consensus sequence of TRE(AP-1)(5'-TGACTCA-3'), by addition of one nucleotide. As there is no direct evidence that TPA stimulates the transcription of rat TRH gene, and there is no study to define TRE of the rat TRH gene, we performed Northern blot assay, transient gene expression study and gel shift assay to identify TRE. TRH mRNA expression of CA77 cells was increased about 2-2.5 fold 30 min after TPA stimulation. When PC12 cells were stimulated by TPA after transfection of the plasmids containing serially deleted 5'upstream of the rat TRH gene ligated to luciferase gene, the transcription of luciferase gene was increased more than 3.2 fold with the plasmid pTRH(-600/84)Luc and pTRH(-113/84)Luc. However, the transcriptional activation was remarkably decreased less than 1.6 fold with pTRH(-77/84)Luc, pTRH(-47/84)Luc, and pTRH(6/84)Luc. The plasmid containing the sequence of -108/-79 did not show any significant activation in both of basal and TPA-stimulated transcription, whereas the plasmid containing the sequence of -70/-41 showed a slight but significant transcriptional activation by TPA. The plasmid containing the sequence of -114/-47 showed remarkable increase in basal transcription and TPA induced transcription of luciferase gene. Gel shift assay revealed that the oligonucleotides spanning -108/-79 and -70/-41 bound to c-Jun, whereas the oligonucleotides spanning -40/1, 1/30, 31/60, 61/84 did not bind. The oligonucleotide of -70/-41 bound to c-Jun with higher affinity compared to that of -108/-79. The one base pair mutant of -70/-41(deletion of C from the middle of TGACCTCA) bound to c-Jun with higher affinity, whereas the one base pair replaced mutant(C to G) bound with lower affinity compared to the wild type oligonucleotide. These results suggest that the rat TRH gene expression is stimulated by TPA to a smaller degree compared to that of other genes, and the two elements act cooperatively as TRE. The downstream TRE variant is mainly responsible for TPA response and c-Jun binding, and the upstream variant play a permissive role for transcriptional activation. The addition of one nucleotide C in the downstream element may be responsible for the relatively lower response of the rat TRH gene to TPA.

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