GROWTH-HORMONE INDUCES TYROSINE PHOSPHORYLATION BUT DOES NOT ALTER INSULIN-LIKE GROWTH-FACTOR-I GENE-EXPRESSION IN HUMAN IM9 LYMPHOCYTES

被引:18
作者
CLAYTON, PE [1 ]
DAY, RN [1 ]
SILVA, CM [1 ]
HELLMANN, P [1 ]
DAY, KH [1 ]
THORNER, MO [1 ]
机构
[1] UNIV VIRGINIA,SCH MED,DEPT MED,CHARLOTTESVILLE,VA 22908
关键词
D O I
10.1677/jme.0.0130127
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
GH induces hepatic IGF-I synthesis by increasing transcription of its gene. IGF-I is synthesized, however, in many other tissues where the effect of GH on its gene expression is less well characterized. IGF-I and GH are produced by human lymphocytes and may function as autocrine regulators of lymphoproliferation. We have therefore used the human IM9 lymphocyte cell line to (A) define the IGF-I gene transcripts expressed and (B) investigate the effect of GH on tyrosine phosphorylation) and (protein (changes in IGF-I mRNA levels) events in intracellular signal transduction. Multiple IGF-I mRNA species, ranging in size from 0.9 to 5.8 kb, were detected by Northern hybridization of poly(A)(+) mRNA from IM9 cells. The human IGF-I gene contains at least six exons and alternative splicing produces a number of transcripts. Solution hybridization with exon-specific riboprobes and amplification by PCR using exon-specific primers revealed that multiple transcripts were expressed in IM9 cells, and that exon 2 was the dominant leader exon. Treatment of IM9 cells with 200 ng recombinant human (rh)GH/ml led to the specific tyrosine phosphorylation of three intracellular proteins (93, 120 and 134 kDa), which are involved in the initial signalling of the GH transduction pathway. However a solution hybridization assay using the IGF-IA specific riboprobe on IM9 cell RNA from similar experiments revealed that GH treatment did not change IGF-I gene expression. This study has demonstrated (A) that the IGF-I gene is expressed in human IM9 lymphocytes, (B) that in contrast to other human tissue, exon 2 is the major leader exon, and (C) that rhGH induces tyrosine phosphorylation of 93, 120 and 134 kDa proteins but does not alter IGF-I gene expression. The IM9 cell may form an important model to investigate a GH transduction pathway not coupled to the IGF-I gene.
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页码:127 / 136
页数:10
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