Opposite regulatory effects of TRPC1 and TRPC5 on neurite outgrowth in PC12 cells
Dae Keon Heo1, Woo Young Chung, Hyun Woo Park
1Department of Pharmacology and Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea.
Abstract:
The transient receptor potential (TRPC) family of Ca²⁺ permeable, non-selective cation channels is abundantly expressed in the brain, and can function as store-operated (SOC) and store-independent channels depending on their interaction with the ER Ca²⁺ sensor STIM1. TRPC1 and TRPC5 have critical roles in neurite outgrowth, however which of their functions regulate neurite outgrowth is unknown. In this study, we investigated the effects of TRPC channels and their STIM1-induced SOC activity on neurite outgrowth of PC12 cells. We report that PC12 cell differentiation down-regulates TRPC5 expression, whereas TRPC1 expression is retained. TRPC1 and TRPC5 interact with STIM1 through the STIM1 ERM domain. Transfection of TRPC1 and TRPC5 increased the receptor-activated Ca²⁺ influx that was markedly augmented by the co-expression of STIM1. Topical expression of TRPC1 in PC12 cells markedly increased neurite outgrowth while that of TRPC5 suppressed neurite outgrowth. Suppression of neurite outgrowth by TRPC5 requires the channel function of TRPC5. However, strikingly, multiple lines of evidence show that the TRPC1-induced neurite outgrowth was independent of TRPC1-mediated Ca²⁺ influx. Thus, a) TRPC1 and TRPC5 similarly increased Ca²⁺ influx but only TRPC1 induced neurite outgrowth, b) the constitutively STIM1(D76A) mutant that activates Ca²⁺ influx by TRPC and Orai channels did not increase neurite outgrowth, c) co-expression of TRPC5 with TRPC1 suppressed the effect of TRPC1 on neurite outgrowth, d) and most notable, channel-dead pore mutant of TRPC1 increased neurite outgrowth to the same extent as TRPC1(WT). Suppression of TRPC1-induced neurite outgrowth by TRPC5 was due to a marked reduction in the surface expression of TRPC1. We conclude that the regulation of neurite outgrowth by TRPC1 is independent of Ca²⁺ influx and TRPC1-promoted neurite outgrowth depends on the surface expression of TRPC1. It is likely that TRPC1 acts as a scaffold at the cell surface to assemble a signaling complex to stimulate neurite outgrowth.
Insights
Transient Receptor Potential Canonical (TRPC) channels influence neurite outgrowth. TRPC1 promotes neurite outgrowth independently of calcium influx, acting as a cell surface scaffold, while TRPC5 suppresses it.
Area of Science:
- Neuroscience
- Cell Biology
- Ion Channel Physiology
Background:
- Transient Receptor Potential Canonical (TRPC) channels are Ca²⁺ permeable cation channels crucial for neuronal function.
- TRPC1 and TRPC5 are implicated in neurite outgrowth, but their specific roles and regulatory mechanisms remain unclear.
- TRPC channels interact with Stromal Interaction Molecule 1 (STIM1) to mediate store-operated calcium (SOC) entry.
Purpose of the Study:
- To investigate the distinct roles of TRPC1 and TRPC5 in neurite outgrowth of PC12 cells.
- To determine the involvement of STIM1-induced SOC activity in TRPC-mediated neurite outgrowth.
- To elucidate the molecular mechanisms by which TRPC1 and TRPC5 regulate neurite extension.
Main Methods:
- PC12 cells were transfected with TRPC1 and TRPC5 constructs.
- Calcium influx was measured using Ca²⁺ imaging techniques.
- Neurite outgrowth was quantified following TRPC channel expression and STIM1 co-expression.
- Mutant channel constructs (channel-dead TRPC1, constitutively active STIM1) were employed to dissect functional roles.
Main Results:
- PC12 cell differentiation altered TRPC5 and TRPC1 expression levels.
- TRPC1 and TRPC5 expression increased Ca²⁺ influx, further enhanced by STIM1 co-expression.
- TRPC1 expression significantly promoted neurite outgrowth, whereas TRPC5 expression suppressed it.
- TRPC1-induced neurite outgrowth was independent of Ca²⁺ influx, as evidenced by channel-dead TRPC1 mutants.
- TRPC5 suppressed TRPC1's effect by reducing TRPC1 surface expression.
Conclusions:
- TRPC1 promotes neurite outgrowth through a Ca²⁺ influx-independent mechanism, relying on its surface expression.
- TRPC1 likely functions as a scaffold protein at the cell surface to assemble signaling complexes for neurite outgrowth.
- TRPC5 suppresses neurite outgrowth, requiring its channel function, and can interfere with TRPC1's scaffolding role.
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