Annexin II is secreted into the extracellular environment, where, via interactions with specific
proteases and
extracellular matrix proteins, it participates in
plasminogen activation, cell adhesion, and
tumor metastasis and invasion. However, mechanisms regulating
annexin II transport across the cellular membrane are unknown. In this study, we used coimmunoprecipitation to show that
Annexin-II was bound to
insulin and
insulin-like growth factor-1 (IGF-1) receptors in PC12 cells and NIH-3T3 cells overexpressing
insulin (NIH-3T3(IR)) or
IGF-1 receptor (NIH-3T3(IGF-1R)). Stimulation of
insulin and
IGF-1 receptors by
insulin caused a temporary dissociation of
annexin II from these receptors, which was accompanied by an increased amount of extracellular
annexin II detected in the media of PC12, NIH-3T3(IR), and NIH-3T3(IGF-1R) cells but not in that of untransfected NIH-3T3 cells. Activation of a different
growth factor receptor, the
platelet-derived growth factor receptor, did not produce such results.
Tyrphostin AG1024, a
tyrosine kinase inhibitor of
insulin and
IGF-1 receptor, was shown to inhibit
annexin II secretion along with reduced receptor phosphorylation. Inhibitors of a few downstream signaling
enzymes including
phosphatidylinositol 3-kinase, pp60c-Src, and
protein kinase C had no effect on
insulin-induced
annexin II secretion, suggesting a possible direct link between receptor activation and
annexin II secretion. Immunocytochemistry revealed that
insulin also induced transport of the membrane-bound form of
annexin II to the outside layer of the cell membrane and appeared to promote cell aggregation. These results suggest that the
insulin receptor and its signaling pathways may participate in molecular mechanisms mediating
annexin II secretion.