CXCR5 is a
serpentine receptor implicated in cell migration in lymphocytes and differentiation in leukocytes. It causes MAPK pathway activation and has known membrane partners for signaling. CXCR5
mRNA is reportedly expressed in neutrophils following isolation, but its role in this cellular context is unknown. CXCR5 is also expressed in HL-60 cells, a human
acute myeloid leukemia line, following treatment with
all-trans retinoic acid, which induces differentiation toward a neutrophil-like state. CXCR5 is necessary for this process; differentiation was crippled in CXCR5 knockout cells and enhanced in cells ectopically expressing it. Since CXCR5 has various
membrane protein partners, we investigated whether CXCR5-driven
all-trans retinoic acid-induced differentiation depends on its association with such partners. Pursuing this, we generated HL-60 cells overexpressing the
protein. We found that CXCR5 drove migration toward its
ligand, CXCL13, and probed for interactions with several candidates using flow cytometry-based Förster resonance energy transfer. Surprisingly, we did not detect interactions with any candidates, including three reported in other cellular contexts. Additionally, we observed no significant changes in
all-trans retinoic acid-induced differentiation; this may be due to the stoichiometry of CXCR5 and partner receptors or CXCL13. The anticipated membrane partnerings were surprisingly apparently unnecessary for downstream CXCR5 signaling and
all-trans retinoic acid-induced differentiation.