p66Shc deficiency enhances CXCR4 and CCR7 recycling in CLL B cells by facilitating their dephosphorylation-dependent release from β-arrestin at early endosomes

Abstract

Neoplastic cell traffic abnormalities are central to the pathogenesis of chronic lymphocytic leukemia (CLL). Enhanced CXC chemokine receptor-4 (CXCR4) and chemokine receptor-7 (CCR7) recycling contributes to the elevated surface levels of these receptors on CLL cells. Here we have addressed the role of p66Shc, a member of the Shc family of protein adaptors the expression of which is defective in CLL cells, in CXCR4/CCR7 recycling. p66Shc reconstitution in CLL cells reduced CXCR4/CCR7 recycling, lowering their surface levels and attenuating B-cell chemotaxis, due to their accumulation in Rab5 endosomes as serine-phosphoproteins bound to β-arrestin. This results from the ability of p66Shc to inhibit Ca and PP2B-dependent CXCR4/CCR7 dephosphorylation and β-arrestin release. We also show that ibrutinib, a Btk inhibitor that promotes leukemic cell mobilization from lymphoid organs, reverses the CXCR4/CCR7 recycling abnormalities in CLL cells by increasing p66Shc expression. These results, identifying p66Shc as a regulator of CXCR4/CCR7 recycling in B cells, underscore the relevance of its deficiency to CLL pathogenesis and provide new clues to the mechanisms underlying the therapeutic effects of ibrutinib.

New Insights on the Emerging Genomic Landscape of CXCR4 in Cancer: A Lesson from WHIM

“…In hematological malignancies, as well as in solid tumors, the overexpression of CXCR4 is responsible for metastasis in organs expressing high CXCL12 levels (e.g., lymph nodes and BM), in addition to disease progression, increased tumor cell survival, and chemoresistance [99]. In chronic lymphocytic leukemia (CLL), the CXCL12/CXCR4 axis induces immune suppression via Signal Transducer and Activator of Transcription 3 (STAT3) phosphorylation in B and T-CLL cells [100].…”

“…The CXCR4 S338X clonality of ≥ 25% represents a potential biomarker for inferior responses to ibrutinib therapy [114]. Responses to ibrutinib and survival are not only impacted by MYD88 L265P but also by CXCR4 mutations [100]. A few drugs targeting CXCR4 are currently under investigation, as the response rates with ibrutinib alone are lower in the patient population with mutated CXCR4 compared to those who have the CXCR4 signature [127,128].…”

Regulation of Selective B Cell Autophagy by the Pro-oxidant Adaptor p66SHC

“…By functioning as a rheostat in cell commitment to apoptosis or autophagy, p66SHC may play an important role both in maintaining cell homeostasis under physiological growth conditions and in fine-tuning cell viability under stress. It should be underscored that the expression of p66SHC can be modulated in response to both physiological and pharmacological stimuli (Migliaccio et al, 1999;Patrussi et al, 2018). Additionally, the pro-oxidant activity of p66SHC is regulated post-translationally by S36 phosphorylation, a process strongly affected by cellular stress (Migliaccio et al, 1999;Nemoto and Finkel, 2002;Pinton et al, 2007).…”

“…This complex, which includes the phosphatases SHP-1 (Src homology phosphatase-1) and SHIP-1 (SH2 domain-containing inositol 5 -phosphatase-1), impairs actin cytoskeleton reorganization in response to CXCR4 or CXCR5 engagement, which limits B cell adhesion to integrin ligands and migration toward the respective chemokines (Patrussi et al, 2014). Additionally, in B cells p66SHC slows down recycling to the plasma membrane of the chemokine receptors CXCR4 and CCR7, which results in a decrease in their surface levels, by preventing the Ca 2+ -dependent transit of internalized receptors from early to recycling endosomes (Patrussi et al, 2018; Figure 1B). Since lymphocytes acquire survival signals during their cyclic traffic through secondary lymphoid organs, the modulation of chemokine receptor signaling by p66SHC at multiple steps contributes to its ability to negatively regulate lymphocyte survival.…”

“…The pro-oxidant activity of p66SHC is also implicated in this function as it is able to modulate in opposite directions the expression of the homing receptor CCR7 and of the sphingosine-1 phosphate receptor S1PR1, which drives B cell exit from lymphoid tissues. Excessive expression and signaling by homing receptors, together with defective expression of S1PR1, favor the residency of the p66SHC-deficient leukemic cells in the pro-survival and chemioprotective lymphoid niche (Capitani et al, 2010;Patrussi et al, 2018Patrussi et al, , 2019.…”