Specific titin and myomesin domains stimulate myoblast proliferation

Abstract

Myofibrillar proteins titin and myomesin stimulated myoblast proliferation as determined by MTT-test and labelled thymidine incorporation in the DNA. Specific Fn type III and Ig-like domains of these proteins were able to exert mitogenic effects as well. Proliferative effect of Fn type III domains was highly sensitive to inhibition of Ca²⁺/calmodulin dependent protein kinase, whereas the effect of Ig-like domains showed greater sensitivity to the inhibition of adenylyl cyclase - cAMP - PKA pathway. IGF-1 autocrine signalling inhibition partially suppressed mitogenic effects revealed by both domain types.

Keywords: Fn type III domain; IGF-1; Ig-like domain; Myoblast proliferation; Myomesin; Titin.

Fig. 1

Induction of the proliferation of murine myoblasts by titin and myomesin. Murine myoblasts were incubated with tested proteins taken at 5 μg/ml concentration (A, B) or with myomesin and titin taken at concentrations from 0 to 25 μg/ml (C, D). MTT-test (A, C; n=8) and [³H]-thymidine incorporation in DNA measurement (B, D; n=6) were performed after 48 h and 24 h incubation, respectively. Graph represents the mean±s.e. Significantly different from control values: **p<0.01.

Fig. 2

Induction of the proliferation of human myoblasts by specific titin and myomesin domains. Human myoblasts were incubated with tested myofibrillar protein domains taken at 5 μg/ml concentration (A, B) or with domains My5, My11-13, TM4 and TA170 taken at concentrations from 0 to 25 μg/ml (C, D). MTT-test (A, C; n=8) and [³H]-thymidine incorporation in DNA measurement (B, D; n=6) were performed after 48 h and 24 h incubation, respectively. Graph represents the mean±s.e. Significantly different from control values: **p<0.01.

Fig. 3

Decrease of mitogenic effects of titin and myomesin domains by the inhibitors of major signalling pathways. Human myoblasts were incubated with domains My5 or My11-13 or TM4 or TA170 taken at 5 μg/ml concentration with or without 10 μM of dideoxyadenosine (DDA) or 100 μM Rp-cAMPS or 10 μM KN93 or 2 μM PQ401 or 10 μg/ml antibodies (AB) to IGF-1. MTT-test (A, C; n=8) and [³H]-thymidine incorporation in DNA measurement (B, D; n=6) were performed after 48 h and 24 h incubation, respectively. Graph represents the mean±s.e. Significantly different from values in samples without inhibitors: *p<0.05, **p<0.01.