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The role of polyamines in somatomedin-stimulated differentiation of L6 myoblasts

✍ Scribed by Daina Z. Ewton; Bradley G. Erwin; Anthony E. Pegg; James R. Florini

Publisher: John Wiley and Sons
Year: 1984
Tongue: English
Weight: 969 KB
Volume: 120
Category: Article
ISSN: 0021-9541
DOI: 10.1002/jcp.1041200302

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✦ Synopsis

The somatomedins are potent stimulators of proliferation and differentiation of cultured myoblasts. In studies on the mechanism($ of these actions, we have measured the activities of ornithine decarboxylase (ODC), an enzyme associated with rapid cell proliferation, and creatine kinase (CK), a biochemical marker for muscle differentiation, after treatment of L6 myoblast cultures with Multiplication Stimulating Activity (MSA), a member of the somatomedin family of insulinlike growth factors. ODC levels reached a peak 24 hours after MSA addition (before any detectable differentiation of the myoblasts) and then decreased as differentiation commenced and CK activity increased. Addition of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, caused a dramatic decrease in differentiation. Measurement of 3Hthymidine incorporation, DNA content, and cell number established that the effect of DFMO on differentiation was not a simple consequence of its antiproliferative actions. Cellular levels of putrescine and spermidine (but not sperrnine) decreased substantially following addition of DFMO to the cultures. The inhibitory effects of DFMO were abolished upon addition of exogenous polyamines to the medium. However, addition of polyamines in the absence of MSA or DFMO did not mimic the stimulation of differentiation by MSA. We conclude that polyamines play an essential role in the stimulation of L6 mvoblast differentiation bv somatomedins, but they are not sufficient to effect this stimulation. We previously demonstrated that the somatomedins are potent stimulators of both growth and differentiation of L6 muscle cells in culture (Florini et al., 1977; Ewton and Florini, 1980, 1981). Addition of somatome-

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