CD44

The CD44 protein is a cell-surface glycoprotein involved in cell-cell interactions, cell adhesion and migration. It is a receptor for hyaluronic acid and can also interact with other ligands, such as osteopontin, collagens, and matrix metalloproteinases (MMPs). A specialized sialofucosylated glycoform of CD44 called HCELL is found natively on human hematopoietic stem cells, and is a highly potent E-selectin and L-selectin ligand. HCELL functions as a "bone homing receptor", directing migration of human hematopoietic stem cells and mesenchymal stem cells to bone marrow.

This protein participates in a wide variety of cellular functions including lymphocyte activation, recirculation and homing, hematopoiesis, and tumor metastasis. Transcripts for this gene undergo complex alternative splicing that results in many functionally distinct isoforms, however, the full length nature of some of these variants has not been determined. Alternative splicing is the basis for the structural and functional diversity of this protein, and may be related to tumor metastasis. Splice variants of CD44 on colon cancer cells display the HCELL glycoform, which mediates binding to vascular E-selectin under hemodynamic flow conditions, a critical step in colon cancer metastasis. CD44 gene transcription is at least in part activated by beta catenin and Wnt signalling (also linked to tumour development). The protein is a determinant for the Indian blood group system.


 * CD44, along with CD25, is used to track early T cell development in the thymus.


 * CD44 expression is an indicative marker for effector-memory T-cells. It is tracked with CFSE chemical tagging.

In addition, variations in CD44 are reported as cell surface markers for some breast and prostate cancer stem cells, and has been seen as an indicator of increased survival time in epithelial ovarian cancer patients.