Human homologues of the Caenorhabditis elegans cell polarity protein PAR6 as an adaptor that links the small GTPases Rac and Cdc42 to atypical protein kinase C.
BACKGROUND
Asymmetric cell division in the Caenorhabditis elegans embryos requires products of par (partitioning defective) genes 1-6 and atypical protein kinase C (aPKC), whereas Cdc42 and Rac, members of the Rho family GTPases, play an essential role in cell polarity establishment in yeast and mammalian cells. However, little is known about a link between PAR proteins and the GTPases in cell polarization.


RESULTS
Here we have cloned cDNAs for three human homologues of PAR6, designated PAR6alpha, beta and gamma, comprising 345, 372 and 376 amino acids, respectively. The PAR6 proteins harbour a PDZ domain and a CRIB-like motif, and directly interact with GTP-bound Rac and Cdc42 via this motif and with the aPKC isoforms PKCiota/lambda and PKCzeta via the N-terminal head-to-head association. These interactions are not mutually exclusive, thereby allowing the PAR6 proteins to form a ternary complex with the GTPases and aPKC, both in vitro and in vivo. When PAR6 and aPKC are expressed with a constitutively active form of Rac in HeLa or COS-7 cells, these proteins co-localize to membrane ruffles, which are known to occur at the leading edge of polarized cells during cell movement.


CONCLUSIONS
Human PAR6 homologues most likely play an important role in the cell polarization of mammalian cells, by functioning as an adaptor protein that links activated Rac and Cdc42 to aPKC signalling.
Noda
Y
Y
Department of Molecular and Structural Biology, Kyushu University Graduate School of Medical Science, Fukuoka 812-8582, Japan.
Takeya
R
R
Ohno
S
S
Naito
S
S
Ito
T
T
Sumimoto
H
H
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D017173:Caenorhabditis elegans / Q000166:cytology / Q000196:embryology* / Q000235:genetics; D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism*; D016764:Cell Polarity; D017931:DNA Primers; D018076:DNA, Complementary; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D011506:Proteins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; C512642:par-6 protein, C elegans; D011493:Protein Kinase C; D020744:rac GTP-Binding Proteins