Functional development of Src tyrosine kinases during evolution from a unicellular ancestor to multicellular animals

doi:10.1073/pnas.0600021103

Functional development of Src tyrosine kinases during evolution from a unicellular ancestor to multicellular animals

*Department of Oncogene Research, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan;
^‡Department of Cell Biology, Biozentrum University of Basel, CH-4056 Basel, Switzerland;
^§Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan;
^¶Laboratory of Molecular Oncology, Osaka Bioscience Institute, Osaka 567-0085, Japan;
^‖JT Biohistory Research Hall, Takatsuki, Osaka 569-1125, Japan; and
**Science and Engineering, Waseda University, Tokyo 169-8555, Japan

Edited by Harold E. Varmus, Memorial Sloan–Kettering Cancer Center, New York, NY, and approved June 17, 2006
↵ ^†Y.S., H.S., N.I., and C.O. contributed equally to this work. (received for review January 2, 2006)

Abstract

The Src family of tyrosine kinases play pivotal roles in regulating cellular functions characteristic of multicellular animals, including cell–cell interactions, cell-substrate adhesion, and cell migration. To investigate the functional alteration of Src kinases during evolution from a unicellular ancestor to multicellular animals, we characterized Src orthologs from the unicellular choanoflagellate Monosiga ovata and the primitive multicellular sponge Ephydatia fluviatilis. Here, we show that the src gene family and its C-terminal Src kinase (Csk)-mediated regulatory system already were established in the unicellular M. ovata and that unicellular Src has unique features relative to multicellular Src: It can be phosphorylated by Csk at the negative regulatory site but still exhibits substantial activity even in the phosphorylated form. Analyses of chimera molecules between M. ovata and E. fluviatilis Src orthologs reveal that structural alterations in the kinase domain are responsible for the unstable negative regulation of M. ovata Src. When expressed in vertebrate fibroblasts, M. ovata Src can induce cell transformation irrespective of the presence of Csk. These findings suggest that a structure of Src required for the stable Csk-mediated negative regulation still is immature in the unicellular M. ovata and that the development of stable negative regulation of Src may correlate with the evolution of multicellularity in animals.

Footnotes

^††To whom correspondence should be addressed. E-mail: okadam{at}biken.osaka-u.ac.jp
Author contributions: Y.S., N.I., C.O., T.M., and M.O. designed research; Y.S., H.S., N.I., C.O., and M.O. performed research; H.S., N.I., T.A., and T.M. contributed new reagents/analytic tools; Y.S., H.S., N.I., C.O., and M.O. analyzed data; and M.O. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. AB049592–AB049594, AB049596, AB098168, AB099494, AB099495, AB006558, and AB098164).
Abbreviation:

REF-T,

rat embryonic fibroblast.