|
Fig. 2
Zebrafish Cxcl12 ligands activate CXCR4 signaling in human cancer cells. Human CXCL12 was aligned to the zebrafish homologs using ClustalW (A). Amino acid residues were conserved in the receptor binding region and activation motif of CXCL12/Cxcl12 chemokines (A,B). Asterisks (*) represent fully conserved residues; colons (:) and periods (.) indicate positions at which residues share strong or weak similarity, respectively. (C,D) Human CXCL12-α and zebrafish ligands Cxcl12a and Cxcl12b induced calcium flux in MDA-MB-231-B cells, as detected by increased fluorescence intensity. The human ligand initiated an immediate response that extinguished rapidly (31s to register half fluorescence intensity after the highest response), whereas the zebrafish ligands triggered a slower and prolonged signal induction (>55s for zCxcl12a and >52s for zCxcl12b to register half fluorescence intensity). (C) The fold intensity increase is calculated by normalization on fluorescence intensity correspondent to signal before response activation. (D) Frames show intensity before signaling activation was triggered by each ligand and at the highest peak of response. The time length to reach the strongest response is indicated.