Downregulation of HtrA1 Promotes Resistance to Anoikis and Peritoneal Dissemination of Ovarian Cancer Cells

Abstract

We previously identified serine protease HtrA1 as a down-regulated gene in epithelial ovarian cancer (EOC), but the functional consequence of loss of HtrA1 in EOC remains largely unclear. Here, we report that loss of HtrA1 attenuates anoikis - a critical physiological barrier for tumor metastasis. In response to loss of anchorage, HtrA1 expression was up-regulated in SKOV3 cells, resulting in autocatalytic activation of HtrA1. Stable knockdown of HtrA1 in SKOV3 and TOV21G cells resulted in resistance to anoikis due to enhanced activation of EGFR/AKT pathway. In suspended SKOV3 cells, enhanced expression of HtrA1 inhibited EGFR/AKT pathway, leading to increased cell death, while protease inactive mutant HtrA1 failed to result in either the inhibition of EGFR/AKT pathway or increased cell death, suggesting the requirement of HtrA1 protease activity in regulating anoikis. Immunoprecipitation and immunofluorescence assays revealed that HtrA1 interacted with EGFR not only on the cell membrane but also in the nucleus. Most importantly, down-regulation of HtrA1 significantly enhanced the peritoneal dissemination of SKOV3ip1 cells in NOD/SCID mice, with increased p-EGFR level in corresponding tumor nodules compared to that in xenografts originated from the control cells. Taken together, these data reveal for the first time a novel function of HtrA1 in promoting anoikis by attenuating activation of EGFR/AKT pathway that may contribute to its metastasis suppression capacity, thus providing a possible explanation for the aggressive nature of human ovarian tumors with down-regulated HtrA1.

Divergent Roles of PAX2 in the Etiology and Progression of Ovarian Cancer

“…HTRA1 is a putative tumor suppressor gene that is downregulated in ovarian cancers (39) and enhances chemosensitivity by targeting the antiapoptotic protein XIAP for degradation (40). Downregulation of HTRA1 enhanced peritoneal dissemination in a xenograft study by increasing phosphorylation of EGFR, AKT, and ERK1/2 (22). We found that Htra1 Research.…”

“…Interestingly, PAX2 expression reduced STOSE colony formation in soft agar, indicating a higher rate of anoikis. This may be attributed to HTRA1 induction, which has been shown to prevent metastasis by inducing anoikis (22). Thus, HTRA1 induction might cause the decreased metastasis seen in PAX2-expressing STOSE tumors.…”

“…5E). HTRA1 has been associated with EGFR activity (22), but RM tumors showed no EGFR expression. Despite the lack of EGFR, PAX2 decreased the levels of PTEN and increased phospho-AKT in the RM tumors ( Fig.…”

Anoikis evasion in inflammatory breast cancer cells is mediated by Bim-EL sequestration

“…[18][19][20] Interestingly, previous studies have shown that ErbB2 and EGFR, which are hyperactivated in a substantial percentage of IBC patients, 21 can effectively antagonize the anoikis program to facilitate anchorage-independent growth. [22][23][24][25][26][27][28] However, a detailed examination of the molecular mechanisms underlying anoikis inhibition in IBC cells has yet to be completed. In this study, we demonstrate that signaling from EGFR and ErbB2 through ERK/MAPK has a major role in the ability of IBC cells to survive in the absence of ECM attachment.…”

HTRA1 (HtrA serine peptidase 1)

“…However, processed forms of HtrA1 have been found in the cytoplasm and in the nuclear fraction (Clawson et al, 2008;Chien et al, 2009;He et al, 2010).…”