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Small GTPase RhoB is involved in cisplatin resistance in human laryngeal carcinoma cells

Acquired resistance to cisplatin represents a major obstacle to successful chemotherapy. Since our cisplatin-resistant CA3ST and CK2 cells display cytoskeleton alterations comparing to parental human laryngeal carcinoma HEp-2 cells, we studied the role of Rho GTPases, which act as major regulators of actin cytoskeleton, in the cellular response to cisplatin. Among several Rho GTPases analyzed, RhoB expression was downregulated in cisplatin-resistant sublines on both mRNA and protein level, as determined by semiquantitative RT-PCR and Western blot, respectively. In addition, immunocytochemistry revealed that cellular localization of RhoB in HEp-2 and CA3ST cells was altered after cisplatin treatment. Transient transfection of EGFP-RhoB in CA3ST cells increased cisplatin-induced cell death measured by flow cytometry, while silencing of RhoB expression with siRNA decreased sensitivity of HEp-2 cells to cisplatin, as determined by MTT assay. Pretreatment with lovastatin, hydroxymethylglutaryl coenzyme A reductase inhibitor that blocks prenylation and activation of Rho GTPases, restored sensitivity of resistant cells to cisplatin to the level found in parental cells. Lovastatin treatment induced concentration-dependent increase in RhoB and cell cycle arrest in G1 phase, which was more pronounced in CA3ST and CK2 cells, whereas at later time points cisplatin-resistant cells were highly susceptible to apoptosis. Since cisplatin-resistant human cervical carcinoma and melanoma cells also showed decreased RhoB expression, we speculate that downregulation of RhoB could be a general phenomena accompanying cisplatin resistance. Therefore, we conclude that RhoB is involved in response of laryngeal carcinoma cells to cisplatin, as well as resistance development to this chemotherapeutic drug. Moreover, since lovastatin has already entered clinical trials for several types of cancer, these data could lead to new clinical strategies aimed to overcome cisplatin resistance and improve efficacy of cancer treatment.

RhoB; cisplatin; drug-resistance; lovastatin

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