Bisphosphorylated PEA-15 Sensitizes Ovarian Cancer Cells to Paclitaxel by Impairing the Microtubule-Destabilizing Effect of SCLIP

Abstract

Paclitaxel is a standard chemotherapeutic agent for ovarian cancer. PEA-15 (phosphoprotein enriched in astrocytes-15 kDa) regulates cell proliferation, autophagy, apoptosis, and glucose metabolism and also mediates AKT-dependent chemoresistance in breast cancer. PEA-15's functions are tightly regulated by its phosphorylation status at Ser104 and Ser116. However, the effect of PEA-15 phosphorylation status on chemosensitivity of cancer cells remains unknown. Here, we tested the hypothesis that PEA-15 phosphorylated at both Ser104 and Ser116 (pPEA-15) sensitizes ovarian cancer cells to paclitaxel. We first found that knockdown of PEA-15 in PEA-15-high-expressing HEY and OVTOKO ovarian cancer cells resulted in paclitaxel resistance, whereas re-expression of PEA-15 in these cells led to paclitaxel sensitization. We next found that SKOV3.ip1-DD cells (expressing phosphomimetic PEA-15) were more sensitive to paclitaxel than SKOV3.ip1-AA cells (expressing nonphosphorylatable PEA-15). Compared to SKOV3.ip1-vector and SKOV3.ip1-AA cells, SKOV3.ip1-DD cells displayed reduced cell viability, inhibited anchorage-independent growth, and augmented apoptosis when treated with paclitaxel. Furthermore, HEY and OVTOKO cells displayed enhanced paclitaxel sensitivity when transiently overexpressing phosphomimetic PEA-15 and reduced paclitaxel sensitivity when transiently overexpressing nonphosphorylatable PEA-15. These results indicate that pPEA-15 sensitizes ovarian cancer cells to paclitaxel. cDNA microarray analysis suggested that SCLIP (SCG10-like protein), a microtubule (MT)-destabilizing protein, is involved in pPEA-15-mediated chemosensitization. We found that reduced expression and possibly posttranslational modification of SCLIP following paclitaxel treatment impaired SCLIP's MT-destabilizing effect, thereby promoting induction of mitotic arrest and apoptosis by paclitaxel. Our findings highlight the importance of pPEA-15 as a promising target for improving the efficacy of paclitaxel-based therapy in ovarian cancer.

UNC-45A is preferentially expressed in epithelial cells and binds to and co-localizes with interphase MTs

“…Interestingly, the OVTOKO ovarian cancer cell line is highly resistant to paclitaxel and can be sensitized to the drug by increasing MT stability via inhibition of the MT-stabilizing protein SCLIP. 22 The potential therapeutic applications of this discovery include consideration of strategies such as sequential or concurrent use of such MT-stabilizing protein inhibitors with other drugs in patients with paclitaxel-resistant ovarian cancers. This finding provides opportunity for further studies to investigate this potential novel avenue.…”

Development of PEA-15 using a potent non-viral vector for therapeutic application in breast cancer

“…We observed that PEA-15 levels were significantly reduced in breast tumor tissues compared to their normal counterparts. The function of PEA-15 as tumor suppressor or as inhibitor of tumor cell growth and invasion in various cancers has been investigated[8; 9; 17; 18]. Our group and others reported that phosphorylation status of PEA-15 is associated with the anti-tumor functions of PEA-15.…”

“…Based on these observations, we proposed that unphosporylated-PEA-15 at both Ser104 and Ser116 could result in more potent suppression of tumorigenicity than wild-type PEA-15 in breast cancer. We have shown that the double-unphosphorylated form (PEA-15-AA), strongly inhibited tumor growth and Ki-67 expression in an ovarian cancer xenograft model[8; 9]. Several other studies also have shown that unphosphorylated form of PEA-15 acts as a tumor suppressor in cervical cancer and lung cancer cells [26; 27].…”

“…Recently, our studies showed that PEA-15 (phosphoprotein enriched in astrocytes) is a multifunctional protein, which can regulate cell proliferation, autophagy, and apoptosis[7; 8; 9]. PEA-15 controls cell proliferation by interfering with the extracellular signal–regulate kinase (ERK) pathway[10].…”

Engineering and cytosolic delivery of a native regulatory protein and its variants for modulation of ERK2 signaling pathway

“…Whereas phosphorylated PEA‐15 has a negligible inhibitory effect on the function of ERK2, non‐phosphorylated PEA‐15 is known to directly bind to ERK2 and block its functions, such as substrate binding and nuclear translocation (Callaway, Abramczyk, Martin, & Dalby, ; Krueger, Chou, Glading, Schaefer, & Ginsberg, ; Trencia et al, ). With such a function, PEA‐15 itself has gained significant attention as a potential therapeutic for cancer treatment (Lee et al, ; Xie et al, ; Xie et al, ). The development of PEA‐15 as a therapeutic agent has several barriers, however, such as a low binding affinity (∼3.4 μM) for ERK2 and the lack of an efficient intracellular delivery system (Mace et al, ).…”