Diverse regulation of full-length and truncated growth hormone receptor expression in 3T3-L1 adipocytes.
Two truncated forms of growth hormone (GH) receptor (GHR), 1-277 and 1-279, were reported to be normally produced in human tissues by alternative splicing in exon 9 and its boundary. We found previously that GHR-277 exerts a dominant-negative effect on full-length GHR (GHR-fl)-mediated GH signaling causing short stature. The existence of truncated GHRs (hGHR-tr) in normal tissues suggests that hGHR-tr may play a physiological role in regulation of GH action at the cellular level. To clarify the physiological significance of GHR-tr and the regulation mechanism of GHR-tr expression, we examined the expression of mouse GHR-tr (mGHR-tr) mRNA in mouse adipocyte 3T3-L1 cells, comparing with that of mouse GHR-fl (mGHR-fl). The mRNAs of two mGHR-tr, mGHR-282 and mGHR-280, were detected by RT-PCR methods using specific primers. Although the mGHR-282 and mGHR-280 mRNA levels were approximately 100 times lower than that of mGHR-fl in mature 3T3-L1 cells, quantitative analysis by competitive RT-PCR methods revealed that the mRNA levels of mGHR-280 in 3T3-L1 cells were transiently reduced and thereafter increased during differentiation from preadipocyte to adipocyte. In contrast, the mRNA levels of mGHR-fl were increased in parallel with the progress of differentiation. Stimulation by GH of differentiated 3T3-L1 mature adipocytes resulted in dose-dependent increases of the mRNA of both mGHR-fl and mGHR-282, whereas it caused a paradoxical decrease of the mRNA of mGHR-280 stimulated by high concentration of GH. These findings suggest that the expressions of truncated mGHRs were regulated in a different manner from that of mGHR-fl, thereby modulating GH action in murine adipocytes.
Iida
Keiji
K
Division of Endocrinology/Metabolism, Neurology and Hematology/Oncology, Department of Clinical Molecular Medicine, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan. iidak2@aol.com
Takahashi
Yutaka
Y
Kaji
Hidesuke
H
Yoshioka
Shiro
S
Murata
Masahiro
M
Iguchi
Genzo
G
Okimura
Yasuhiko
Y
Chihara
Kazuo
K
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D017398:Alternative Splicing; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D048429:Cell Size; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D051379:Mice; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism*
D020033:Protein Isoforms; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone