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Background  PERK eIF2α kinase is required for the proliferation of the insulin-secreting beta- cells as well as insulin synthesis and secretion. In addition, PERK signaling has been found to be an important factor in determining growth and angiogenesis of specific types of tumors, and was attributed to PERK-dependent regulation of the hypoxic stress response. In this report we examine the role of PERK in regulating proliferation and angiogenesis of transformed beta-cells in the development of insulinomas.    Methodology  The SV40 Large T-antigen (Tag) was genetically introduced into the insulin secreting beta-cells of  Perk KO  mice under the control of an inducible promoter. Tumor growth and the related parameters of cell proliferation were measured. In late stage insulinomas the degree of vascularity was determined.    Principal Findings  The formation and growth of insulinomas in  Perk -deficient mice was dramatically ablated with much fewer tumors, which averaged 38-fold smaller than seen in wild-type control mice. Beta-cell proliferation was ablated in  Perk -deficient mice associated with reduced tumor growth. In the small number of large encapsulated insulinomas that developed in  Perk -deficient mice, we found a dramatic reduction in tumor vascularity compared to similar sized insulinomas in wild-type mice. Although insulinoma growth in  Perk -deficient mice was largely impaired, beta-cell mass was increased sufficiently by T-antigen induction to rescue the hypoinsulinemia and diabetes in these mice.    Conclusions  We conclude that PERK has two roles in the development of beta-cell insulinomas, first to support rapid cell proliferation during the initial transition to islet hyperplasia and later to promote angiogenesis during the progression to late-stage encapsulated tumors.

PERK Regulates the Proliferation and Development of Insulin-Secreting Beta-Cell Tumors in the Endocrine Pancreas of Mice