Insulin induces tyrosine dephosphorylation of a 92 kDa protein in suspended monocytes

Monocytes bear insulin receptors similar to those expressed in other tissues, but insulin action in these cells remains unclear. There is evidence that adhesion, by generating a complex array of irreversible transformations, may modify the response of cells to other stimuli, such as hormones. The present study aimed to characterise the pattern of insulin induced tyrosine phosphorylation of monocytes in suspension. Monocytes in suspension were obtained by sequential gradient centrifugation and the tyrosine phosphoproteins were analyzed by immunoblot with antiphosphotyrosine antibodies. The major result of the study is that in suspended monocytes insulin induced a dose and time dependent dephosphorylation of a protein with a molecular mass of about 92 kDa without stimulating the tyrosine phosphorylation of the Insulin Receptor Substrat-1 (IRS-1). In conclusion, we showed that in monocytes in suspension insulin seems to activate a tyrosine phosphatase, which, in turn, dephosphorylates a protein with an apparent molecular weight of 92 kDa.