Loss of compensatory pro-survival and anti-apoptotic modulator, IKKε, sensitizes ovarian cancer cells to CHEK1 loss through an increased level of p21

Abstract

Ovarian cancer (OC) is extremely heterogeneous, implying that therapeutic strategies should be specifically designed based on molecular characteristics of an individual's tumor. Previously, we showed that IKKε promotes invasion and metastasis in a subset of OCs. Here, we identified CHEK1 as an IKKε-dependent lethal gene from shRNA kinome library screen. In subsequent pharmacological intervention studies, the co-inhibition of IKKε and CHEK1 was more effective in killing OC cells than single treatment. At the molecular level, co-inhibition dramatically decreased pro-survival proteins, but increased proteins involved in DNA damage and apoptosis. IKKε-knockdown increased p21 levels, while overexpression of wild-type IKKε, but not a kinase dead IKKε mutant decreased p21 levels. We further demonstrated that the depletion of p21 rendered OC cells more resistant to cell death induced by co-inhibition of IKKε and CHEK1. In conclusion, we revealed a novel interplay between IKKε, CHEK1 and p21 signaling in survival of OC. Our study provides a rationale for the clinical development of specific IKKε inhibitor and for usage of IKKε as an exploratory marker for resistance to CHEK1 inhibitors in the clinic. The interplay provides one potential explanation as to why very few clinical responses were achieved in patients treated with single-agent CHEK1 inhibitors.

Identification of CHEK1, SLC26A4, c-KIT, TPO and TG as new biomarkers for human follicular thyroid carcinoma

“…Additional cell cycle regulator CDKN1B was significantly downregulated in PDTCs (Table 2). Finally, we demonstrate that the apoptosis related gene BCL2, previously reported to be associated with a number of malignancies by other groups [16, 17], exhibits a downregulation in FTC, PTC and PDTC, with a progressive increase in fold change associated with malignancy progression (Table 5, [8]).…”

“…Alterations in CHEK1 levels have been previously described by us in PTC (Table 5, [8]), and in a number of non-thyroid malignancies by other groups [16, 17]. A recent report reveals that CHEK2 (but not CHEK1 ) levels are altered in PDTC and ATC [18].…”

Topotecan synergizes with CHEK1 (CHK1) inhibitor to induce apoptosis in ovarian cancer cells

“…Since HGS ovarian cancer cells required higher concentrations of TPT than non-HGS cells, we sought to identify a combination that achieved maximal cytotoxic effect with a minimal dose of TPT. We previously found that CHEK1 was overexpressed in most HGS ovarian cancers [ 6 ], and hypothesized that inhibition of CHEK1 would increase the therapeutic index of TPT, given its importance in DNA damage repair pathways. Therefore, we investigated whether CHEK1 inhibitor, PF477736, sensitized HGS ovarian cancer cell lines to TPT treatment.…”

“…We recently found that CHEK1 gene was overexpressed in most of HGS ovarian cancer, and combined inhibition of pro-survival modulator, IKKε, cooperatively induced apoptosis in ovarian cancers [ 6 ]. In this study, we have further extended this finding to evaluate CHEK1 inhibitor-based combination therapy.…”

“…In HSG ovarian cancers, p53 is either null or mutated, increasing the cellular dependency on CHEK1/2 for DNA damage repair and survival. Supporting this notion, we recently showed that CHEK1 gene is overexpressed in nearly all cases of HGS ovarian cancer as compared to normal ovarian surface epithelium in The Cancer Genome Atlas (TCGA) dataset, suggesting that CHEK1 is required for cells to tolerate the defective DNA repair intrinsic to HGS cancers [ 2 , 6 ]. Upon DNA damage, CHEK1 is activated by ATR signaling and sequentially phosphorylated at residues S317 and S345 which subsequently induce autophosphorylation on S296 to trigger cell cycle arrest and DNA repair [ 7 ].…”