CXCL12 is commonly known as SDF-1, with two variants, SDF-1α (89 amino acids) and SDF-1β (93 amino acids) derived from alternative splicing. They have identical amino acid sequences, differing only by the addition of four amino acids at the carboxy-terminus of the β form. CXCL12α and β are ubiquitously expressed, and it has been suggested that their activity is regulated through differential proteolytic processing. Proteases present in serum process CXCL12α initially at the carboxy-terminus (through carboxypeptidase N) and subsubsequently at the amino-terminus (through CD26); while CXCL12β is only processed at the amino-terminus. These proteolytic processes affect the chemokine's ability to bind to heparin and cells as well as its ability to stimulate proliferation and chemotaxis. CXCL12α is inactivated by other enzymes such as metalloproteases, serine proteases, and leukocyte elastase. CXCL12/CXCR4 interactions play a key role in maintaining proliferation and survival of bone marrow stem cell subpopulations under stress conditions. Also, CXCL12 is highly expressed in bone marrow stromal stem cells and regulates growth and survival. CXCL12 promotes survival by inducing anti-apoptotic proteins, decreasing apoptotic proteins, and increasing transcription of cell survival genes. Data suggests that CXCL12β mediates cells' survival by enhancing autophagy in bone marrow mesenchymal stem cells.