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First published online 8 July 2008
doi: 10.1242/jcs.026682

Journal of Cell Science 121, 2473-2480 (2008)
Published by The Company of Biologists 2008
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Research Article

The secreted Dictyostelium protein CfaD is a chalone

Deenadayalan Bakthavatsalam, Debra A. Brock, N. Neda Nikravan, Kevin D. Houston, R. Diane Hatton and Richard H. Gomer*

Department of Biochemistry and Cell Biology, MS-140, Rice University, 6100 S. Main Street, Houston, TX 77005-1892, USA

* Author for correspondence (e-mail: richard{at}rice.edu)

Accepted 30 April 2008

Dictyostelium discoideum cells secrete CfaD, a protein that is similar to cathepsin proteases. Cells that lack cfaD proliferate faster and reach a higher stationary-phase density than wild-type cells, whereas cells that overexpress CfaD proliferate slowly and reach the stationary phase when at a low density. On a per-nucleus basis, CfaD affects proliferation but not growth. The drawback of not having CfaD is a reduced spore viability. Recombinant CfaD has no detectable protease activity but, when added to cells, inhibits the proliferation of wild-type and cfaD– cells. The secreted protein AprA also inhibits proliferation. AprA is necessary for the effect of CfaD on proliferation. Molecular-sieve chromatography indicates that in conditioned growth medium, the 60 kDa CfaD is part of a ~150 kDa complex, and both chromatography and pull-down assays suggest that CfaD interacts with AprA. These results suggest that two interacting proteins may function together as a chalone signal in a negative feedback loop that slows Dictyostelium cell proliferation.

Key words: Autocrine factor, Chalone, Cell number counting, Tissue size






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