Human substance P receptor lacking the C‐terminal domain remains competent to desensitize and internalize

Substance P receptor (SPR) and its naturally occurring splice‐variant, lacking the C‐terminal tail, are found in brain and spinal cord. Whether C‐terminally truncated SPR desensitizes like full‐length SPR is controversial. We used a multivaried approach to determine whether human SPR (hSPR) and a C‐terminally truncated mutant, hSPRΔ325, differ in their desensitization and internalization. In HEK‐293 cells expressing either hSPRΔ325 or hSPR, SP‐induced desensitization of the two receptors was similar when measured by inositol triphosphate accumulation or by transient translocation of coexpressed PKCβII‐GFP to the plasma membrane. Moreover, translocation of β‐arrestin 1 or 2‐GFP (βarr1‐GFP or βarr2‐GFP) to the plasma membrane, and receptor internalization were also similar. However, hSPR and hSPRΔ325 differ in their phosphorylation and in their ability to form β‐arrestin‐containing endocytic vesicles. Unlike hSPR, hSPRΔ325 is not phosphorylated to a detectable level in intact HEK293 cells, and whereas hSPR forms vesicles containing either βarr1‐GFP or βarr2‐GFP, hSPRΔ325 does not form any vesicles with βarr1‐GFP, and forms fewer vesicles with βarr2‐GFP. We conclude that truncated hSPR undergoes agonist‐dependent desensitization and internalization without detectable receptor phosphorylation.