Characterization of a new WHIM syndrome mutant reveals mechanistic differences in regulation of the chemokine receptor CXCR4

Jiansong Luo,Francesco De Pascali,G Wendell Richmond,Amer M Khojah,Jeffrey L Benovic

doi:10.1016/j.jbc.2021.101551

Abstract

WHIM syndrome is a rare immunodeficiency disorder that is characterized by warts, hypogammaglobulinemia, infections, and myelokathexis. While several gain-of-function mutations that lead to C-terminal truncations, frame shifts and point mutations in the chemokine receptor CXCR4 have been identified in WHIM syndrome patients, the functional effect of these mutations are not fully understood. Here, we report on a new WHIM syndrome mutation that results in a frame shift within the codon for Ser339 (S339fs5) and compare the properties of S339fs5 with wild-type CXCR4 and a previously identified WHIM syndrome mutant, R334X. The S339fs5 and R334X mutants exhibited significantly increased signaling compared to wild-type CXCR4 including agonist-promoted calcium flux and extracellular-signal-regulated kinase activation. This increase is at least partially due to a significant decrease in agonist-promoted phosphorylation, β-arrestin binding, and endocytosis of S339fs5 and R334X compared with wild-type CXCR4. Interestingly, there were also significant differences in receptor degradation, with S339fs5 having a very high basal level of degradation compared with that of R334X and wild-type CXCR4. In contrast to wild-type CXCR4, both R334X and S339fs5 were largely insensitive to CXCL12-promoted degradation. Moreover, while basal and agonist-promoted degradation of wild-type CXCR4 was effectively inhibited by the CXCR4 antagonist TE-14016, this had no effect on the degradation of the WHIM mutants. Taken together, these studies identify a new WHIM syndrome mutant, CXCR4-S339fs5, which promotes enhanced signaling, reduced phosphorylation, β-arrestin binding and endocytosis, and a very high basal rate of degradation that is not protected by antagonist treatment.

Highlights

WHIM syndrome is a rare, genetic disease, which is named for its four key clinical manifestations, Warts, Hypogammaglobulinemia, recurrent Infections, and Myelokathexis [1]
CXCR4 has been extensively investigated and implicated in several diseases besides WHIM syndrome including acquired immunodeficiency syndrome (AIDS), where it serves as a coreceptor for human immunodeficiency virus (HIV), and cancer, where it has a role in metastasis [18, 19]
We report on a new patient cohort containing a mutation in CXCR4 that results in a frame shift within the codon for Ser339 (S339fs5) (Fig. 1)

Summary

Introduction

WHIM syndrome is a rare, genetic disease, which is named for its four key clinical manifestations, Warts, Hypogammaglobulinemia, recurrent Infections, and Myelokathexis [1]. One WHIM syndrome patient has been identified with a defect in the protein kinase GRK3 resulting in increased CXCL12-promoted signaling and impaired desensitization and internalization [16, 17]. Characterization of a new WHIM syndrome mutant agonist-dependent phosphorylation of the receptor by GRKs and protein kinase C (PKC), desensitization mediated by β-arrestin binding, ubiquitination by the E3 ubiquitin ligase AIP4, endocytosis, and sorting to lysosomes where the receptor is degraded [14, 23,24,25,26].

Results

Conclusion