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A Naturally Occurring Splice Variant of CXCL12/Stromal Cell-Derived Factor 1 Is a Potent Human Immunodeficiency Virus Type 1 Inhibitor with Weak Chemotaxis and Cell Survival Activities

Jeffrey D. Altenburg, Hal E. Broxmeyer, Qingwen Jin,^, Scott Cooper, Sunanda Basu, and Ghalib Alkhatib^*

Department of Microbiology and Immunology and the Walther Oncology Center, Indiana University School of Medicine, 635 Barnhill Drive, Room 420, Indianapolis, Indiana 46202, and the Walther Cancer Institute, Indianapolis, Indiana 46208

Received 7 February 2007/ Accepted 1 May 2007

CXCL12/stromal cell-derived factor 1 is a member of the CXC family of chemokines that plays an important role in hematopoiesis and signals through CXCR4 and CXCR7. Two splice variants of human CXCL12 (CXCL12 and CXCL12ß) induce chemotaxis of CXCR4⁺ cells and inhibit X4 infection. Recent studies described four other novel splice variants of human CXCL12; however, their antiviral activities were not investigated. We constructed and expressed all of the CXCL12 splice variants in Escherichia coli. Recombinant proteins were purified through a His affinity column, and their biological properties were analyzed. All six CXCL12 variants induced chemotaxis of CXCR4⁺ and CXCR7⁺ cell lines. Enhancement of survival and replating capacity of human hematopoietic progenitor cells were observed with CXCL12, CXCL12ß, and CXCL12 but not with the other variants. CXCL12 showed the greatest antiviral activity in X4 inhibition assays and the weakest chemotaxis activity through CXCR4. The order of potency in X4 inhibition assays was as follows: CXCL12 > CXCL12ß > CXCL12 > CXCL12 > CXCL12 > CXCL12. The order of anti-human immunodeficiency virus (HIV) activity was associated with the number of BBXB motifs present in each variant; the most potent inhibitor was CXCL12, with five BBXB domains. The results suggest that the different C termini of CXCL12 variants may contain important molecular determinants for the observed differences in antiviral effects and other biological functions. These studies implicate CXCL12 as a potent HIV-1 entry inhibitor with significantly reduced chemotaxis activity and small or absent effects on progenitor cell survival or replating capacity, providing important insight into the structure-function relationships of CXCL12.

Published ahead of print on 16 May 2007.

Present address: Department of Neurology, Nanjing Medical University, Nanjing, Jiangsu Province, China 210029.