Department of Biochemistry and Molecular Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
Section of Allergy and Immunology, Department of Medicine, Rush University Medical Center, Chicago, Illinois, USA.
J Biol Chem. 2022 Feb;298(2):101551. doi: 10.1016/j.jbc.2021.101551. Epub 2021 Dec 30.
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.
WHIM 综合征是一种罕见的免疫缺陷疾病，其特征为疣、低丙种球蛋白血症、感染和髓过氧化物酶缺乏。虽然已经在 WHIM 综合征患者中鉴定出几种导致趋化因子受体 CXCR4 的 C 末端截断、移码和点突变的获得性功能突变，但这些突变的功能影响尚不完全清楚。在这里，我们报告了一种新的 WHIM 综合征突变，该突变导致丝氨酸 339 处的密码子发生移码（S339fs5），并比较了 S339fs5 与野生型 CXCR4 和先前鉴定的 WHIM 综合征突变体 R334X 的特性。与野生型 CXCR4 相比，S339fs5 和 R334X 突变体表现出明显增强的信号转导，包括激动剂促进的钙流和细胞外信号调节激酶激活。这种增加至少部分是由于与野生型 CXCR4 相比，S339fs5 和 R334X 激动剂促进的磷酸化、β-抑制蛋白结合和内化显著减少所致。有趣的是，受体降解也存在显著差异，与 R334X 和野生型 CXCR4 相比，S339fs5 具有非常高的基础降解水平。与野生型 CXCR4 相反，R334X 和 S339fs5 对 CXCL12 促进的降解基本上不敏感。此外，虽然野生型 CXCR4 的基础和激动剂促进的降解可被 CXCR4 拮抗剂 TE-14016 有效抑制，但这对 WHIM 突变体的降解没有影响。总之，这些研究鉴定了一种新的 WHIM 综合征突变体 CXCR4-S339fs5，它促进了增强的信号转导、降低的磷酸化、β-抑制蛋白结合和内化以及非常高的基础降解率，而这种降解率不受拮抗剂治疗的保护。
