The effect of insulin and IGF1 on the cytoskeleton in relation to SMC migration

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The cytoskeleton is a complex network of protein filaments extending throughout the cytoplasm that is involved in a range of cell processes. Of the three main

Actin Cytoskeleton And Insulin

10 min after insulin 10 imin after insulin + diltiazem

FIG. 2. Insulin-induced F-actin reorganization near the membrane of human vascular smooth muscle cells showing a ruffling which does not appear when Ca2+ channels of these cells are blocked by diltiazem. The results are similar in the case of IGF1 (unpublished).

10 min after insulin 10 imin after insulin + diltiazem

FIG. 2. Insulin-induced F-actin reorganization near the membrane of human vascular smooth muscle cells showing a ruffling which does not appear when Ca2+ channels of these cells are blocked by diltiazem. The results are similar in the case of IGF1 (unpublished).

cytoskeletal types, the actin filaments are primarily responsible for many cell movements, for example for SMC migration (Alberts et al 1994, p 787—803). According to Bretscher's model of fibroblast locomotion, actin filaments depolymerize ahead of the nucleus, generating actin subunits which diffuse to the cell's front where actin filaments polymerize at the leading edge (Bretscher 1996). Chemoattractant receptors contribute to the promotion of actin assembly at the leading cell edge (Stossel 1993). Ca2+ ions play an important role in the process of assembly and deassembly of actin filaments. Insulin induces these specific rearrangements in mesangial cells in vitro. Fluorescent staining for F-actin with phalloidin normally shows actin filaments spanning the entire cell in all directions. After insulin treatment, the cells show peripheral ru¥ing and lifting off from the substrate as attachments are released (Berfield et al 1996). We have shown that insulin, like IGF1, induces membrane ru¥ing of F-actin in human vascular SMCs in vitro. This effect appears very quickly, just 5 minutes after hormone application. As expected, the blockade of Ca2+ channels by diltiazem does not allow insulin to induce ruffling (Fig. 2). The result is similar for IGF1.

These data suggest that insulin influences SMC movements with a mechanism probably similar to that of IGF1.

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