DISSOCIATION OF CHEMOTAXIS FROM AGONIST-INDUCED RECEPTOR INTERNALIZATION IN A LYMPHOCYTE CELL-LINE TRANSFECTED WITH CCR2B - EVIDENCE THAT DIRECTED MIGRATION DOES NOT REQUIRE RAPID MODULATION OF SIGNALING AT THE RECEPTOR LEVEL

To investigate the role of the carboxyl-terminal region (52 amino acid s) of the monocyte chemoattractant protein 1 receptor (CCR2B) in chemo taxis, we created a series of mutants and expressed them in a murine p re-B lymphocyte cell Line. Truncation of the cytoplasmic carboxyl tail to 20 amino acids had little or no effect on chemotaxis or signal tra nsduction, but further truncation resulted in marked functional defect s. Upon incubation with monocyte chemoattractant protein 1, CCR2B unde rwent rapid and extensive internalization, and this was impaired progr essively as the carboxyl tail was truncated from 52 to 8 amino acids. Mutation of all of the serine and threonine residues in the carboxyl t ail to alanine also resulted in markedly impaired receptor internaliza tion but did not affect signaling or chemotaxis. We conclude that the membrane-proximal portion of the cytoplasmic carboxyl tail of CCR2B is critically involved in chemotaxis and signal transduction, but neithe r phosphorylation of carboxyl serines or threonines nor internalizatio n of the receptor is required for robust chemotaxis.