Measurement of Phosphoinositide 3-Kinase Activation by Interleukins
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				Phosphoinositide 3-kinases (PI 3-kinases) are an evolutionarily conserved family of lipid kinases that have attracted much attention over the past 10 years or so (reviewed in ref.
				1
				). Three PI 3-kinase classes have been defined on the basis of primary structure, regulation, and their in vitro lipid substrate specificity. Class I PI 3-kinases interact with Ras and form heterodimeric complexes with adaptor proteins that link them to different upstream signaling events (
				1
				). They are able to convert phosphatidylinositol (PtdIns), PtdIns(
				4
				)
				P
				, and PtdIns(
				4
				,
				5
				)
				P
				2
				into PtdIns(
				3
				)
				P
				, PtdIns(
				3
				,
				4
				)
				P
				2
				, and PtdIns(
				3
				,
				4
				,
				5
				)
				P
				3
				, respectively, by phosphorylating the D-3 position of the inositol head groups of phosphoinositide lipids (collectively known as D-3 phosphoinositide lipids and shown in Fig. 1 ) (
				1
				,
				2
				).
				
				
			
		
					Fig. 1. 
					(
					A
					) Schematic representation of the structure of D-3 phosphoinositide lipids. (
					B
					) Routes for synthesis of PtdIns(
					3
					)
					P
					, PtdIns(
					3
					,
					5
					)
					P
					2
					, PtdIns(
					3
					,
					4
					)
					P
					2
					, and PtdIns(
					3
					,
					4
					,
					5
					)
					P
					3
					.
				
				








