p62 protein is expressed in pancreatic beta cells

p62 is a cellular protein that plays an adapter role in signal transduction pathways involved in such diverse biological functions as proliferation, differentiation, reaction to oxidative stress and immune response. Furthermore, p62 has recently been detected as a component of intracytoplasmic protein aggregates (inclusion bodies), which are hallmarks of a variety of chronic degenerative disorders, such as Parkinson's disease and Alzheimer's disease, but also of steatohepatitis. Here we report that p62 and insulin are co-expressed in a diffuse fashion in beta cells in normal human pancreas as well as in primary chronic pancreatitis and in normal pancreas from mouse and swine. In contrast, p62 protein is absent from, or only focally and very weakly expressed in, insulinomas, glucagonomas or non-functioning pancreatic neuroendocrine tumours or carcinomas that express insulin or other pancreatic as well as extrapancreatic hormones. Although the biological function of p62 in beta cells is unknown, the co-expression of p62 and insulin in non-neoplastic beta cells suggests that, in the beta cell, p62 may play a role in specific insulin-related signalling. Since p62 may also be involved in pro-apototic signal transduction, the loss of p62 expression in neuroendocrine neoplasms of the pancreas may render the tumour cells less sensitive to pro-apototic signals. Further research is necessary to elucidate the role of p62 in beta cell-specific signal transduction.