Oncogene database

10848

PPP1R13L

protein phosphatase 1, regulatory subunit 13 like;PPP1R13L;protein phosphatase 1, regulatory subunit 13 like

NFkB interacting protein 1|NFkB-interacting protein 1|PPP1R13B-like protein|inhibitor of ASPP protein|inhibitor of apoptosis stimulating protein of p53|protein iASPP|protein phosphatase 1, regulatory (inhibitor) subunit 13 like|relA-associated inhibitor|r

19q13.32

protein-coding

We have previously shown that ASPP1 and ASPP2 are specific activators of p53; one mechanism by which wild-type p53 is tolerated in human breast carcinomas is through loss of ASPP activity. We have further shown that 53BP2, which corresponds to a C-terminal fragment of ASPP2, acts as a dominant negative inhibitor of p53 (ref. 1). Hence, an inhibitory form of ASPP resembling 53BP2 could allow cells to bypass the tumor-suppressor functions of p53 and the ASPP proteins. Here, we characterize such a protein, iASPP (inhibitory member of the ASPP family), encoded by PPP1R13L in humans and ape-1 in Caenorhabditis elegans. iASPP is an evolutionarily conserved inhibitor of p53; inhibition of iASPP by RNA-mediated interference or antisense RNA in C. elegans or human cells, respectively, induces p53-dependent apoptosis. Moreover, iASPP is an oncoprotein that cooperates with Ras, E1A and E7, but not mutant p53, to transform cells in vitro. Increased expression of iASPP also confers resistance to ultraviolet radiation and to cisplatin-induced apoptosis. iASPP expression is upregulated in human breast carcinomas expressing wild-type p53 and normal levels of ASPP. Inhibition of iASPP could provide an important new strategy for treating tumors expressing wild-type p53.

iASPP is a member of the apoptosis-stimulating proteins of p53 (ASPP) family and negatively regulates the apoptotic function of p53. In a hematopoietic system, overexpression of iASPP results in blockage of apoptosis, which may play a role in regulating hematopoietic stem cell (HSC) numbers. To address this, we first analyzed the expression of iASPP in patients with acute leukemia (AL) and found it was highly expressed in patients with AL. We further established a transgenic mouse model in which human iASPP was specifically expressed in hematopoietic cells. Overexpression of iASPP led to an increase in the proportion of long-term HSCs, short-term HSCs, multipotent progenitors, and common myeloid progenitor. HSCs from iASPP transgenic mice had an advantage in long-term reconstitution potential. In addition, the hematopoietic cells from iASPP transgenic mice exhibited a significantly lower level of p53 dependent apoptosis. After irradiation damage, hematopoietic cells of iASPP transgenic mice had a higher level of gamma-H2AX expression, which lasted for a longer time. These results provide the first evidence that the iASPP can increase HSC populations and reconstitution capacity. Interestingly, in response to cell damage stimuli, hematopoietic cells can be protected against apoptosis by iASPP; meanwhile these apoptosis-resistant cells would have more mutation accumulation, which might be the potential risk for malignant transformation.-Jia, Y., Peng, L., Rao, Q., Xing, H., Huai, L., Yu, P., Chen, Y., Wang, C., Wang, M., Mi, Y., Wang, J. oncogene iASPP enhances self-renewal of hematopoietic stem cells and facilitates their resistance to chemotherapy and irradiation.