Hematopoietic progenitor cells and cellular microenvironment: Behavioral and molecular changes upon interaction

Cell-cell contact between stem cells and cellular determinants of the microenvironment plays an essential role in controlling cell division. Using human hematopoietic progenitor cells (CD34(+)/CD38(-)) and a stroma cell line (AFT024) as a model, we have studied the initial behavioral and molecular sequel of this interaction. Time-lapse microscopy showed that CD34(+)/CD38(-) cells actively migrated toward and sought contact with stroma cells and 30% of them adhered firmly to AFT024 stroma through the uropod. CD44 and CD34 are collocalized at the site of contact. Gene expression profiles of CD34(+)/CD38(-) cells upon cultivation with or without stroma for 16,20, 48, or 72 hours were analyzed using our human genome cDNA microarray. Chk1, egr1, and cxcl2 were among the first genes upregulated within 16 hours. Genes with the highest upregulation throughout the time course included tubulin genes, ezrin, c1qr1, fos, pcna, mcm6, ung, and dnmt1, genes that play an essential role in reorganization of the cytoskeleton system, stabilization of DNA, and methylation patterns. Our results demonstrate directed migration of CD34(+)/CD38(-) cells toward AFT024 and adhesion through the uropod and that upon interaction with supportive stroma, reorganization of the cytoskeleton system, regulation of cell division, and maintenance of genetic stability represent the most essential steps.