Cloning and Functional Expression of Human Short TRP7, a Candidate Protein for Store-operated Ca²⁺ Influx*

The regulation and control of plasma membrane Ca²⁺ fluxes is critical for the initiation and maintenance of a variety of signal transduction cascades. Recently, the study of transient receptor potential channels (TRPs) has suggested that these proteins have an important role to play in mediating capacitative calcium entry. In this study, we have isolated a cDNA from human brain that encodes a novel transient receptor potential channel termed human TRP7 (hTRP7). hTRP7 is a member of the short TRP channel family and is 98% homologous to mouse TRP7 (mTRP7). At the mRNA level hTRP7 was widely expressed in tissues of the central nervous system, as well as some peripheral tissues such as pituitary gland and kidney. However, in contrast to mTRP7, which is highly expressed in heart and lung, hTRP7 was undetectable in these tissues. For functional analysis, we heterologously expressed hTRP7 cDNA in an human embryonic kidney cell line. In comparison with untransfected cells depletion of intracellular calcium stores in hTRP7-expressing cells, using either carbachol or thapsigargin, produced a marked increase in the subsequent level of Ca²⁺ influx. This increased Ca²⁺ entry was blocked by inhibitors of capacitative calcium entry such as La³⁺ and Gd³⁺. Furthermore, transient transfection of an hTRP7 antisense expression construct into cells expressing hTRP7 eliminated the augmented store-operated Ca²⁺ entry. Our findings suggest that hTRP7 is a store-operated calcium channel, a finding in stark contrast to the mouse orthologue, mTRP7, which is reported to enhance Ca²⁺ influx independently of store depletion, and suggests that human and mouse TRP7 channels may fulfil different physiological roles.