Heterogeneity among RIP‐Tag2 insulinomas allows vascular endothelial growth factor‐A independent tumor expansion as revealed by studies in Shb mutant mice: Implications for tumor angiogenesis

Abstract

The Shb adapter protein is a signaling intermediate that operates downstream of vascular endothelial growth factor receptor-2 (VEGFR-2) in endothelial cells. The Shb knockout mouse displays a dysfunctional microvasculature and impaired growth of subcutaneously implanted tumor cells. We decided to investigate tumor growth and angiogenesis in the absence of Shb in an inheritable tumor model, the RIP-Tag2 mouse, which produces insulinomas in a manner highly dependent on de novo angiogenesis. We observed a reduced tumor incidence and burden in both RIP-Tag2 Shb−/− and RIP-Tag2 Shb+/− mice. This correlated with a reduced microvascular density, measured as a percentage of insulinoma area positive for CD31 staining, and altered vascular morphology. However, treatment with a VEGFA blocking antibody was without effect on the Shb mutant tumor volume whereas it significantly inhibited tumor volume in the wild-type mice, suggesting that in mice with reduced Shb expression tumor angiogenesis was primarily sustained by VEGF-A independent pathway(s). This notion was further substantiated by gene expression analysis of angiogenic markers showing reduced VEGF-A expression in Shb-deficient tumors. Considerable heterogeneity with respect to the gene expression profiles of other angiogenic markers and the signal-transduction characteristics was observed between different tumors, suggesting that multiple “rescue” pathways could be operating. The numbers of invasive tumors or metastases were unchanged in the Shb mutant. It is concluded that the Shb mutant background reduces tumor frequency by chronically suppressing VEGF-A dependent angiogenesis. However, VEGF-A independent angiogenesis supports a significant degree of tumor expansion in Shb-deficient mice, indicating heterogeneity in the mechanisms by which tumor expansion is promoted. Interference with Shb signaling may provide novel means for future cancer therapy.

Aberrant association between vascular endothelial growth factor receptor-2 and VE-cadherin in response to vascular endothelial growth factor-a in Shb-deficient lung endothelial cells

“…They also suggest the involvement of Shb in this process. Indeed, it is clear from our previous publications [10,11,18] that Shb deficiency has consequences for the structure of adherens junctions in vivo and that this has functional implications. The latter is most clearly demonstrated by the altered physiological response to arterial ligation, in which the vascular permeability was reduced 24 hours after the procedure [11].…”

The role of the Src Homology-2 domain containing protein B (SHB) in β cells

“…The properties of this includes: reduced tumor and Matrigel angiogenesis , Akerblom et al 2012, Christoffersson et al 2012, reduced vascular permeability ), an altered vascular architecture (Christoffersson et al 2012), abnormal endothelial and pericyte morphology and ultrastructure , Akerblom et al 2012, Christoffersson et al 2012, reduced blood flow upon ischemia (Christoffersson et al 2012, Nikpour et al 2015 and abnormal properties of leukocyte extravasation (Nikpour et al 2015). Isolated Shb knockout endothelial cells displayed in vitro altered signaling properties with elevated basal FAK, Rac1, Akt, ERK and myosin light chain kinase signaling and reduced ligand (VEGF) responsiveness , Zang et al 2013.…”

“…In that tumor model, VEGFAdependent tumor angiogenesis was reduced by the absence of SHB, causing smaller tumors. However, VEGFA-independent tumor expansion was not affected by Shb deficiency (Akerblom et al 2012). In order to elucidate the underlying mechanisms, Affymetrix microarray analysis on WT and Shb-deficient tumor RNA Table 2.…”

Animal models of spontaneous pancreatic neuroendocrine tumors

“…It is hypothesized that an obligatory "angiogenesis switch" is required for the hyperplasticdysplastic/PNET transition to occur, supported by that vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) inhibitors suppress PNET formation (Casanovas et al, 2005;Gocheva et al, 2010;Åkerblom et al, 2012;Wicki et al, 2012). Thus angiogenesis not only plays an important role in in the transition to PNET but is also a therapeutic target for PNET.…”