Transcriptional regulation of angiogenesis-related puromycin-insensitive leucyl-specific aminopeptidase in endothelial cells

Regulation of ERAP1 and ERAP2 genes and their disfunction in human cancer

The endoplasmic reticulum (ER) aminopeptidases ERAP1 and ERAP2 are two multifunctional enzymes playing an important role in the biological processes requiring trimming of substrates, including the generation of major histocompatibility complex (MHC) class I binding peptides. In the absence of ERAP enzymes, the cells exhibit a different pool of peptides on their surface which can promote both NK and CD8⁺ T cell-mediated immune responses. The expression of ERAP1 and ERAP2 is frequently altered in tumors, as compared to their normal counterparts, but how this affects tumor growth and anti-tumor immune responses has been little investigated. This review will provide an overview of current knowledge on transcriptional and post-transcriptional regulations of ERAP enzymes, and will discuss the contribution of recent studies to our understanding of ERAP1 and ERAP2 role in cancer immunity.

Puromycin insensitive leucyl-specific aminopeptidase (PILSAP) affects RhoA activation in endothelial cells

Puromycin insensitive leucyl-specific aminopeptidase (PILSAP) expressed in endothelial cells (ECs) plays an important role in angiogenesis due to its involvement in migration, proliferation and network formation. Here we examined the biological function of PILSAP with respect to EC morphogenesis and the related intracellular signaling for this process. When mouse endothelial MSS31 cells were cultured, a dominant negative PILSAP mutant converted cell shape to disk-like morphology, blocked stress fiber formation, and augmented membrane ruffling in random directions. These phenotypic changes led us to test whether PILSAP affected activities of Rho family small G-proteins. Abrogation of PILSAP enzymatic activity or its expression attenuated RhoA but not Rac1 activation during cell adhesion. This attenuation of RhoA activation was also evident when G-protein coupled receptors such as proteinase-activated receptor or lysophosphatidic acid receptor were activated in ECs. These results indicate that PILSAP affects RhoA activation and that influences the proper function of ECs.

Puromycin insensitive leucyl-specific aminopeptidase (PILSAP) is required for the development of vascular as well as hematopoietic system in embryoid bodies

We have shown that puromycin insensitive leucyl-specific aminopeptidase (PILSAP) is required for regulation of angiogenesis. However, it remains unclear whether PILSAP plays a role in endothelial cell (EC) differentiation. We examined the role of PILSAP by using an embryoid bodies (EBs) culture system. Fms-like tyrosine kinase-1 (Flk-1) showed two expression peaks on days 4 and 10 of culture. These two peaks represent populations of mesodermal precursors and mature ECs, respectively. Endothelial markers such as VE-cadherin, CD34, CD31 and Tie2 followed the first peak of Flk-1. Interestingly, the expression of PILSAP showed a pattern similar to that of Flk-1. ES cells transfected with mutant PILSAP (mtPILSAP) cDNA of a dominant negative activity organized less vascular structure and showed decreased levels of vascular lineage markers. The similar results were obtained in EBs treated with leucinethiol, a specific inhibitor of leucine aminopeptidase or siRNA for PILSAP. However, Flk-1 expression was unaffected on day 4. The expression of markers for hematopoietic lineage and muscle cells in mtPILSAP-EBs was also reduced. These results suggest that although PILSAP may not function in the initial generation of Flk-1 positive mesodermal precursors, it dose play a role in growth of vascular, hematopoietic, and muscular lineage population from those precursors.