A novel Akt/PKB-related kinase is essential for morphogenesis in Dictyostelium

• Published in: Current biology Vol. 10; no. 12; pp. 708 - 717
• Main Authors: Meili, Ruedi, Ellsworth, Charlene, Firtel, Richard A
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 15.06.2000
• Subjects: Akt protein; Amino Acid Sequence; Animals; Cloning, Molecular; Dictyostelium; Dictyostelium - enzymology; Dictyostelium - growth & development; DNA, Complementary; Gene Expression Regulation, Developmental; Gene Expression Regulation, Enzymologic; Genetic Complementation Test; Molecular Sequence Data; Morphogenesis; PKB protein; PKBR-1 protein; Protein-Serine-Threonine Kinases - chemistry; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Protozoan Proteins; Sequence Homology, Amino Acid
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/S0960-9822(00)00536-4

Background:Dictyostelium Akt/PKB is homologous to mammalian Akt/PKB and is required for cell polarity and proper chemotaxis during early development. The kinase activity of Akt/PKB kinase is activated in response to chemoattractants in neutrophils and in Dictyostelium by the chemoattractant cAMP functioning via a pathway involving a heterotrimeric G protein and PI3-kinase. Dictyostelium contains several kinases structurally related to Akt/PKB, one of which, PKBR-1, is investigated here for its role in cell polarity, movement and cellular morphogenesis during development. Results: PKBR-1 has a kinase and a carboxy-terminal domain related to those of Akt/PKB, but no PH domain. Instead, it has an amino-terminal myristoylation site, which is required for its constitutive membrane localization. Like Akt/PKB, PKBR-1 is activated by cAMP through a G-protein-dependent pathway, but does not require PI3-kinase, probably because of the constitutive membrane localization of PKBR-1. This is supported by experiments demonstrating the requirement for membrane association for activation and in vivo function of PKBR-1. PKBR-1 protein is found in all cells throughout early development but is then restricted to the apical cells in developing aggregates, which are thought to control morphogenesis. PKBR-1 null cells arrest development at the mound stage and are defective in morphogenesis and multicellular development. These phenotypes are complemented by Akt/PKB, suggesting functional overlap between PKBR-1 and Akt/PKB. Akt/PKB PKBR-1 double knockout cells exhibit growth defects and show stronger chemotaxis and cell-polarity defects than Akt/PKB null cells. Conclusions: Our results expand the previously known functions of Akt/PKB family members in cell movement and morphogenesis during Dictyostelium multicellular development. The results suggest that Akt/PKB and PKBR-1 have overlapping effectors and biological function: Akt/PKB functions predominantly during aggregation to control cell polarity and chemotaxis, whereas PKBR-1 is required for morphogenesis during multicellular development.