The cytoplasmic domains of the CNNM family of transmembrane proteins modulate the ion channel-kinase TRPM7.

The ion channel and kinase TRPM7 contributes to a wide range of physiological and pathological processes, yet how it is controlled by signaling pathways remains poorly understood. Members of the CNNM family of transmembrane proteins (CNNM1-4) have been shown to selectively bind and regulate the TRPM7 channel. CNNM binding partners, including the PRL family of proteins (PRL1-3) and ARL15, also modulate TRPM7 channel function. However, the regulation of TRPM7's kinase activity in vivo remains unclear. CNNMs contain a DUF21 transmembrane domain, a CBS-pair domain, followed by a COOH-terminal CNBH domain. Here, we identified multiple interaction sites between TRPM7 and CNNMs. The CNNM transmembrane domain was sufficient to mediate assembly of the CNNM2-TRPM7 complex, while the CBS-pair and CNBH domains provided additional points of contact. Electrophysiological analysis revealed that the CBS-pair domain modulates TRPM7 channel activity. ARL15, a known suppressor of TRPM7 channel function, required the CNNM CBS-pair domain to inhibit channel activity. Additionally, the CNNM2 CNBH domain bound to the TRPM7 kinase domain and modestly enhanced its catalytic activity in vitro. Collectively, these findings demonstrate that the cytoplasmic domains of CNNMs play critical roles in regulating TRPM7 channel and kinase activities.