Lipidation of Hedgehog proteins: function, enzymology and therapeutic potential in pancreatic cancer

Abstract

URL: http://www1.imperial.ac.uk/nhli/molecular/lipidation/ Hedgehog (Hh) proteins (Shh, Dhh and Ihh) are secreted intercellular signallingmolecules important inmammalian development and also in the aetiology of many human cancers, hence the Hh signalling pathway is a popular target for development of anti-cancer therapies (1). Hhs are unique in being dually lipidatedwith aN-terminal amide-linked palmitate and a Cterminal cholesterol, added during its transit through the secretory pathway. Thesemodifications are crucial for assembly intomacromolecular complexes for cell-to-cell transport and also for biological function; nonlipidated Hhs are dramatically less potent than the fully lipidated protein. Hedgehog acyltransferase (Hhat) is the enzyme responsible for palmitoylation of the N-terminal cysteine of Hh proteins, and belongs to the membrane bound O-acyltransferase (MBOAT) protein family. Knockdown experiments in pancreatic ductal adenocarcinoma and non-small cell lung cancer cells demonstrate that Hhat is crucial for Shh palmitoylation, assembly into macromolecular complexes and function as assessed by Hh pathway activation, cell growth and invasion, and para/juxtacrine signalling (2). Our results underline the potential of this enzyme as a target for chemotherapy in diverse human cancers including PDAC. Our work has been greatly facilitated by development of bioorthogonal chemical labels for the palmitate and cholesterol moieties (3). Recent results using these to study novel inhibitors will be presented. Hhat is predicted to have 8-12 transmembrane domains but the true number is not known. We have made recent progress in analysis of the membrane topology of Hhat which will allow us better to understand how it functions, and aid in inhibitor screening. 1. Dlugosz AA, Talpaz M. Following the hedgehog to new cancer therapies. N Engl J Med 2009; 361: 1202-5. 2. Konitsiotis AK, Chang SC, Jovanovic B, Masumoto N, Ciepla P, Palmer CP et al. Attenuation of Hedgehog acyltransferase-catalyzed Sonic hedgehog palmitoylation causes reduced proliferation and invasiveness of human carcinoma cells. PLoSONE in press. 3. Heal WP, Jovanovic B, Bessin S, Wright MH, Magee AI and Tate EW. Bioorthogonal chemical tagging of protein cholesterylation in living cells. Chem Comm 2011; 47: 4081-3. Abstracts / Pancrea e4