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Original Articles
- 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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- 17 Download
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Abstract
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- 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.
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