Circulating Endothelial Progenitor Cells from a patients with renal cell carcinoma display aberrant VEGF regulation, reduced apoptosis and altered ultrastructure

Angiogenesis is a fundamental biological process during development as well as in adult life, both in physiological and pathological conditions, as for example in cancer development. Endothelial Progenitor Cells (EPCs) are cells with self-renewal capacity, able to differentiate into mature Endothelial Cells (ECs) and to generate patent vessels in vivo. EPCs seem to play a fundamental role in the "angiogenic switch", the process which allows the transition from in situ carcinoma to a highly vascularized tumor; therefore, they could be a potential target in the development of new drugs. In our work we compared healthy subjects derived EPCs (N-EPCs) and EPCs isolated from patients with renal cell carcinoma (RCC-EPCs), focusing on frequency, proliferation rate, tubulogenesis ability, apoptosis and ultrastructure. Furthermore, we analyzed EPCs Ca2+ signaling pathway, especially after treatment with VEGF, the principal mitogenic stimulus for EPCs, as we already know that neoplastic transformation is accompanied by a remodeling of the Ca2+ toolkit. We found that circulating EPCs are significantly more frequent in patients, having otherwise the same immunophenotypic profile, overlapping growth curve and tubulogenic capacity. We also showed that RCC-EPCs are more resistant to apoptosis induced by rapamycin. Moreover, VEGF induces NF-kB nuclear translocation in N-EPCs in a Ca2+ dependent manner, increasing related gene and protein expression. Based on the concept that VEGF does not induce Ca2+ oscillation in RCC-EPCs, we showed that RCC-EPCs anyway express a functional VEGF receptor 2 which is not able to induce gene and protein expression, suggesting a possible downstream blockade of the pathway. Finally, we demonstrated that RCC-EPCs has less Ca2+ amount in endoplasmic reticulum and mitochondria, fact that potentially reflects the ultrastructural rearrangement found in RCC-EPCs, with their more widely spaced smooth and rough endoplasmic reticulum and more abundant mitochondria in RCC-EPCs.The results reported in this work strongly highlights circulating EPCs in cancer patients as potential target for new therapies aimed to blocking tumor angiogenesis.