RacGAP1 Is a Novel Downstream Effector of E2F7-Dependent Resistance to Doxorubicin and Is Prognostic for Overall Survival in Squamous Cell Carcinoma

Abstract

We have previously shown that E2F7 contributes to drug resistance in head and neck squamous cell carcinoma (HNSCC) cells. Considering that dysregulation of responses to chemotherapy-induced cytotoxicity is one of the major reasons for treatment failure in HNSCC, identifying the downstream effectors that regulate E2F7-dependent sensitivity to chemotherapeutic agents may have direct clinical impact. We used transcriptomic profiling to identify candidate pathways that contribute to E2F7-dependent resistance to doxorubicin. We then manipulated the expression of the candidate pathway using overexpression and knockdown in in vitro and in vivo models of SCC to demonstrate causality. In addition, we examined the expression of E2F7 and RacGAP1 in a custom tissue microarray (TMA) generated from HNSCC patient samples. Transcriptomic profiling identified RacGAP1 as a potential mediator of E2F7-dependent drug resistance. We validated E2F7-dependent upregulation of RacGAP1 in doxorubicininsensitive SCC25 cells. Extending this, we found that selective upregulation of RacGAP1 induced doxorubicin resistance in previously sensitive KJDSV40. Similarly, stable knockdown of RacGAP1 in insensitive SCC25 cells induced sensitivity to doxorubicin in vitro and in vivo. RacGAP1 expression was validated in a TMA, and we showed that HNSCCs that overexpress RacGAP1 are associated with a poorer patient overall survival. Furthermore, E2F7-induced doxorubicin resistance was mediated via RacGAP1-dependent activation of AKT. Finally, we show that SCC cells deficient in RacGAP1 grow slower and are sensitized to the cytotoxic actions of doxorubicin in vivo. These findings identify RacGAP1 overexpression as a novel prognostic marker of survival and a potential target to sensitize SCC to doxorubicin.

Rho GTPase Transcriptome Analysis Reveals Oncogenic Roles for Rho GTPase-Activating Proteins in Basal-like Breast Cancers

“…Others have refuted this finding, however (37). In BLBC cells, similarly to in squamous cell carcinoma cells (46), knockdown of RacGAP1 caused an increase in cellular RhoA activity. It is possible that RhoA activity may be indirectly altered by the depletion of RacGAP1, for example as a result of mislocalized Ect2 – a RhoA-selective RhoGEF whose localization is otherwise regulated by RacGAP1 (30).…”

miR‐4324‐RACGAP1‐STAT3‐ESR1 feedback loop inhibits proliferation and metastasis of bladder cancer

“…RACGAP1 overexpression is associated with cutaneous squamous cell carcinomas patients’ resistance to doxorubicin and poor prognosis . Doxorubicin is a widely used intravesical chemotherapy drug in BCa treatment .…”

“…RACGAP1 can induce resistance to doxorubicin in squamous cell carcinoma. 13 Doxorubicin is a commonly used chemotherapeutic drug in BCa treatment, particularly in intravesical chemotherapy. 17,18 The increased resistance to doxorubicin is a serious obstacle to its extensive application in BCa treatment.…”

Rac GTPase activating protein 1 promotes oncogenic progression of epithelial ovarian cancer

“…In head and neck squamous cell carcinoma (HNSCC) cells, doxorubicin resistance was reported to be mediated by RacGAP1‐dependent activation of AKT. Knockdown of RacGAP1 in HNSCC cells showed slower growth and sensitized the cytotoxic actions of doxorubicin in mice models . Further experiments are essential to verify its role in the drug resistance of other tumor types, including EOC.…”