Opposite regulation of IGF-I and IGF-I receptor mRNA and concomitant changes of GH receptor and IGF-II/M6P receptor mRNA in human IM-9 lymphoblasts

摘要

Human IM-9 lymphoblasts synthesize IGF-I and express IGF-I receptors, IGF-II/M6P receptors and GH receptors. We have studied the regulation of mRNA expression of IGF-I, IGF-I receptors, IGF-II/M6P receptors and GH receptors in IM-9 cells upon serum-withdrawal and re-addition of serum. IM-9 cells were cultured in RPMI-1640 medium with or without serum for various periods of time. RNA was prepared using guanidinium thiocyanate and CsCl. Antisense riboprobes for human IGF-I, IGF-I receptor, IGF-II/M6P receptor, GH receptor and for comparison for human beta-actin were synthesized and labeled with 32P. Protected fragments of 379 bases and of 420 and 350 bases with the IGF-I receptor and with the IGF-I probe respectively and protected fragments of 670 bases and of 51 and 121 bases with the GH receptor and with the beta-actin probe were detected. For the human IGF-II/M6P receptor probe protected fragments of 260 bases were visualized in RNA samples. The amount of mRNA present in each lane (10 /xg total RNA) was determined by computed densitometry. The amount of IGF-I mRNA expressed by IM-9 cells decreased rapidly (within two hours) and dramatically (more than 120%) after the withdrawal of serum and increased significantly (220%) after the re-addition of serum. This increase of IGF-I mRNA preceded the increase in cell number that was seen after 48 h of medium change. Conversely, the expression of IGF-I receptor mRNA and beta-actin mRNA increased by more than 250% after the withdrawal of serum within 2 and 8 h respectively, while GH receptor mRNA fell within 2-4 h. The expression of IGF-II/M6P receptor mRNA continued to increase throughout the duration of the cell culture experiment. We conclude that IGF-I and IGF-I receptor mRNAs are regulated in an opposite direction in serum-deprived IM-9 lymphoblasts, In addition, GH receptor mRNA expression parallels IGF-I mRNA expression.