Subunit composition of VRAC channels determines substrate specificity and cellular resistance to P t‐based anti‐cancer drugs

Abstract

Although platinum-based drugs are widely used chemotherapeutics for cancer treatment, the determinants of tumor cell responsiveness remain poorly understood. We show that the loss of subunits LRRC8A and LRRC8D of the heteromeric LRRC8 volume-regulated anion channels (VRACs) increased resistance to clinically relevant cisplatin/carboplatin concentrations. Under isotonic conditions, about 50% of cisplatin uptake depended on LRRC8A and LRRC8D, but neither on LRRC8C nor on LRRC8E. Cell swelling strongly enhanced LRRC8-dependent cisplatin uptake, bolstering the notion that cisplatin enters cells through VRAC. LRRC8A disruption also suppressed drug-induced apoptosis independently from drug uptake, possibly by impairing VRAC-dependent apoptotic cell volume decrease. Hence, by mediating cisplatin uptake and facilitating apoptosis, VRAC plays a dual role in the cellular drug response. Incorporation of the LRRC8D subunit into VRAC substantially increased its permeability for cisplatin and the cellular osmolyte taurine, indicating that LRRC8 proteins form the channel pore. Our work suggests that LRRC8D-containing VRACs are crucial for cell volume regulation by an important organic osmolyte and may influence cisplatin/carboplatin responsiveness of tumors.

Specific and essential but not sufficient roles of LRRC8A in the activity of volume-sensitive outwardly rectifying anion channel (VSOR)

“…4E), which has recently been identified as a necessary component of the VSOR-related transport system for blasticidin 32 and Pt-derived anti-cancer drugs, cisplatin and carboplatin. 16 Thus, it is concluded that deficiency of VSOR activity in cisplatin-resistant KCP-4 cells is caused by an asyet-unidentified factor other than LRRC8A/D/E genes. …”

“…26,27 Recently, cisplatin resistance in other cell lines has been shown to be associated with loss of LRRC8D 16 and with reduced expression of LRRC8A. 28,29 Here, we examined whether deficiency of VSOR current generation in KCP-4 cells is related to a lack of or insufficient expression of LRRC8A or LRRC8D.…”

“…15 More recently, Jentsch's group has discovered the roles of LRRC8D in cisplatin and taurine transport and in cisplatin resistance acquirement in human KBM7 cells. 16 LRRC8s may exhibit diverse functions through LRR domain-mediated protein-protein interactions. It has been reported that truncation of LRRD in LRRC8A causes deficiency of B cell development.…”

Inactivation and Anion Selectivity of Volume-regulated Anion Channels (VRACs) Depend on C-terminal Residues of the First Extracellular Loop

“…However, the lack of knowledge of the underlying protein(s) forming these channels has greatly hampered further exploration and verification of their suggested physiological and pathophysiological roles. Only recently, LRRC8 (leucine-rich repeat-containing 8) family proteins, which display four putative transmembrane domains and a large C terminus with up to 17 leucine-rich repeats, have been identified as essential components of VRACs (8,9), and LRRC8 heteromers very likely form the channel pore (6,8,10). The physiological importance of VRACs is underscored by the drastically increased lethality of constitutive Lrrc8a KO mice that display multiple tissue abnormalities (11).…”

“…The physiological importance of VRACs is underscored by the drastically increased lethality of constitutive Lrrc8a KO mice that display multiple tissue abnormalities (11). Moreover, recent studies revealed a role of VRACs in the uptake of certain antibiotics (12) and platinum-based anticancer drugs like cisplatin and in tumor drug resistance (6).…”