Phosphoinositide 3-kinases: A conserved family of signal transducers

t?mtialteract

been described (seven in mammals encoded by three different genes, and one see Fig. 2). They all conin Drosophila; tam two SH2 domains linked by an interSN2 region, which is both necessary and

ot only

(3)P is constitutively present in ic ceils and its levels are largely

also in

homology domar binding partners are unclear. There has been no report to date of a preferential coupling between any of the class I, adaptors and catalytic sutmrnits, a!;hough it is possible t tissue-specific differences in function or

Their intracel

for ~~~os~bo~~ositi~e 3-kinases (P13Ks), which p~~os~bory~ate the bydroxyl group at ~~os~t~~~ 3 on the inositoG ring and induce different signals (Fig. 1). This review will focus on three areas of P13K research in which substantial proFirst, we gress has recently been ma tures and will describe the structural classification of the different P13Ks. Next, we will review recently identified motecules that act ~~$t~earn and downstream of PI3Ks. Finally, we will describe work on P13K in different eukaryotic organisms, and discuss how these studies may contribute to our future understanding ot the function of Pl3K signalling.

3Ks convert Ptdl PtdIns(4,5)Pz to Ptdlns&, Ptdlns(3,4)l’L and Ptdins(3,4,5)P,, respectively (Fig. 1).

. Panayotou and d are at the LudwigInstitute for Cancer Research, ding House Street, London, UK WlP SBT: . D.WaterfIeld is also in the Department of Biochemistry and Molecular Biology, UniversityCollege, Gower Street, London, UK WClE 6BT. Copyright

second messengers (reviewed in Ref. 2). Pf3K Lipid products are not substrates so they are not deinositol phosphates. ases mediate their ccttabolism by removmg the phosphate group at position 3 or 5 of the inositol ring’.:’ [Fig. -I). Several 5phosphatase genes have ow been cloned (for overview, see Ref. 3) and their role in signailing is being elucidated (for example, see Ref. 4).

Pl3K catalytic subunits can be divided into three main classes on the basis of their in vitro lipid substrate specificity, structure and likely mode of regulation Ptdlns(4)P and Ptdlns(4,5)fY In vim, however, their preferred substrate is likely to be Ptdlns(4,5)P,. All mammalian Pl3Ks from this class interact with active, GTP-bound Ras (Refs S-10; R. Wetzker, pers. commun.). Tbey all form heterodimerit complexes with adaptor proteins that link them to different upstream signallingevents. Class 1PlSK catalytic subunits can be subdivided into two subclasses (A and B) according to the type of adap tor subunit with which they associate.

0 1991, E!sevier Science Ltd. All rights reserved.

0968-0004/97/$17.00

are stimulated by G-protein

identified member of this P13K subfamily, ~110~ (Ref. 11) contains an aminoterminal Ras-binding site, a PlK domain and a catalytic domain (Table I). Stephens and co-workers recently reported the isolation of a regulatory ~101 subunit that associates tightly with ~110~ (Ref. 12). This novel adaptor does not display any homology with known proteins and the exact mechanism by which it mediates coupling of pllOy to G proteins remains unknown. Class II P13Ksare larger (> 200 kDa) enzymes that phosphorylate in oitvo Ptdlns and Ptdlns(4)E but not Ptdlns(4,5)P,. Their defining feature is a C2 domain’” at their carboxyl terminus (Table I>. The C2 domains of class 11 P13Ks lack critical Asp residues that coordinate

PII: S0968-0004(9?)01061-X

*Nomenclature used IS accordmg to Ref. 1. Phosphomosltids (PI) IS used as a genericterm. whereas phosphatidylinos6ol (Ptdlns) is used to Indicate specific phosphotnositides. e.g. Ptdlns(3)P.

m33S 22 - JULY 1997

__ ---

--- _--Pt:?s

___ _-

- ~-or

2tdlns

3-kinases 1 1 Ptd/ns(#)P

4-kinases

Ptdlns(4)P

Skinases

b

-

Ptdlns(4,5)Pa

Ptdlns(3,4)Ps

Phosphoinositide

pathways, Ins, inositol;

PI 3.kinases,

binding of Ca”* in the first C2 domain of synaptotagmin13. Consistent with this, a class II P13K has been found to bind lipids in a Ca2’-independent manner14. At present, it is unknown whether class 11 Pl3K activity is regulated by extracellular stimuli. Class III P13Ks have a substrate specificity restricted to Ptdlns. These Pf3Ks are homologous to Vps34p, the only Pl3K present in yeast. Vps34p is essential for the trafficking of newly formed proteins from the Colgi to the vacuole, the equivalent of ihe mammalian lysosome (reviewed in Refs 3, 15. 16). Members of this class of P13Ks also

4

DiacylgByeerol

Pns(l,4,5)&

5-Phosphatases

Ptdlns(3)P

I

C

\

I

I

I

Phos~ho~j~sss

----

Ptdlns(3,4,5)P, ___-

phosphoinositide

3-kinases;

Ptdlns, phosphatidyljnosltol.

occur as heterodimers. Yeast Vps34p is found in complex with VpslSp. a 170 kDa Ser/Thr kinase. which both activates and recruits Vps34p to membranes15. Similarly, human Vps34p associates with e cura 150 kDa Vpsl5p homofogueli. Pf3Ks rent hypothesis is that class and their Ptdlns(3)P lipid product MfiP a housekeeping role in constitutive mem-

sic w iassociated

PllOU. B. ii (rn) BpllO (Om) AGE-l (Ce) PIKI. PIK2 (Dd)

pB5a. B (m) ~55~. y (m) p50tu (m) ~60 (Dm)

~110~ (m) PIK3 (Dd)

plO1 (In)

P13KC2d/Cpkm/p170 Pl3KC2p (m) Pl3K_68D/Cpk (Dm) Pl3K.C2 (Ce)

(e.g.

SW-like) Tyr kinase

Tyr kmases and Ras

C protern By subunrts and Ras

(m) 7

?

vps15p (SC)

Conshtubve?

‘Key of Structural motifs: adaptor-brnding (light purple); Rasbmdmg (green): C2 (yellow); PIK (dark purple): kmase domarn (red). ‘For the proteins other than those derived from yeast. fruit fly and mammals, no brochemrcal proof of Pl3K bptd kmase acbvrty IS avarlable. These enzymes have been allocated to a particular class of Pl3K mainly based on primary sequence homology of the core kinase doma&. The abbreviations used are: m. mammalian: Ce. Caenorhabditis elegans: Dd. Bictyostelium dtscoideum: Om. Drosophila melanogaster: SC. Saccharomyces cerevrsrae. The GenBank/EMBL acceSSfOr numbers for class and II catalytic subunits are: mammalia: pllOo (human: 229090. HSU79143: mouse: U03279: bovine: M93252). pllOp (human: S67334 pll0-f (human: X83368: pig: YiO743). pi106 (human: YlOO55. U57843. U86587: mouse, U86453). Pl3K-C2u (human: Y13367). Cpk-m (also known as p170) (mouse: U52193: U55772), Pl3KC2p (Y13892. Yll312) - D. melanogastec 0~110 (YO9070). Pl3K_680 (also known as Cpk) (X92892: U52192) - C. e/eganS: age-1 (U56101). putative C2domain containing Pl3K (on cosmid 269660) - D. discoideum: PlKl (U23476), PIK2 (U23477) and PIK3 (U23478). Accession numbers for ~101 Vpsl5p and ~150 are Y10742, M59835 and Y08991, respectively. ‘The Prototype of the class ill Pl3Ks is the S. cerevisiae protein Vps34p (X53531). Vps34p homologues from other specres are not shown indwrdually. They are: human Pt3K (246973): D. melanogaster, Pl3K_59F (X99912); C. d/scoideum. PIK5 (U23480): and the Vps34prelated Pl3Ks from Schizosaccharomyces pombe W32583). Soybean (L29770). Arebidopsis thafiana (UlO669) and C. eregans (Y12543).

i

268

i I

activity, and by receptors linked to ~eterot~~~e~~c c pmteiws(fw a listinsg of the sign&x that trigger class I PlM activation,seeR&i 2.an). At present, it is unclearhowG-protein sigmk are Ehyed fnamthe pPasma membrane to the class I,, enzymes. For class 9, PM