The year 2012 sees two papers from IMCB garner more than 1000 citations each. The number of citations is one indicator of a paper’s scientific impact, and in the biological sciences a paper is termed a “Citation Classic” once it has accumulated more than 400 citations. According to ISI# there are 14 such papers published by IMCB groups. Papers with 1000 citations are exceptional, and in the context of Singapore’s relatively new push in biology, only three non-clinical papers have achieved this notable mark (ref 1, 2, 3). Here we highlight one of these publications by the GSK-IMCB group (ref 3).
The other paper – from Alan Porter and his lab – will be featured on this website later.
Edward Manser*, Thomas Leung*, Harfizah Salihuddin*, Zhuo-shen Zhao*, Louis Lim†.
* - Glaxo-IMCB Group, Institute of Molecular & Cell Biology, National University of Singapore, Kent Ridge 0511, Singapore.
- Institute of Neurology, 1 Wakefield Street, London WC1N 1PJ, UK.
In the 1990s Ras emerged as a key regulator of cell proliferation while the Rho proteins (RhoA, Cdc42, Rac1) were found to organize the actin cytoskeleton. How these small 21 kDa GTP binding proteins carried out their respective functions was a mystery. Louis Lim’s lab in collaboration with Alan Hall discovered GAP proteins that could ‘turn off’ Rac in 1991 (ref 4). In developing a new assay to identify Rac GAPs in the brain, Ed Manser made the serendipitous discovery of PAK (p21 activated kinase). This 68 kDa protein bound tightly to Rac1 and acted as an anti-GAP protein; Rac1 in turn directly activates the kinase. PAK1 was fully characterized after a year of painstaking biochemical purification, micro-sequencing and cloning, the latter by the then PhD student Zhao Zhuo-Shen.
The Nature article by Ed and colleagues in the GSK-IMCB group was met with great excitement because it suggested protein kinases could be directly transmitting the signals from Rac1 and Cdc42 to organize actin. Further, the Rac1 binding domain of PAK1 was sequence–related to ACK1 (ref 5), which allowed similar effector proteins to be discovered from primary sequence alone. Raf1 was reported a few months before as a target of the oncogene Ras (ref 6), but unlike PAK1 the Raf1 kinase could not be activated (in vitro) outside the cell. Of course PAK1 and family members turn out to have many cellular functions, but the model of PAK1 activation presented in the 1994 paper has stood the test of time. Subsequently the group has gone on to find the key adaptors which allow PAKs to act at cell adhesions (ref 7) and at the centrosome (ref 8), linking PAK with cell division. One of the most interesting recent discoveries connects PAK1 with the fragile-X protein FMRP (ref 9), whose loss is the most common genetic cause of mental retardation. As PAKs are important for cancer cell migration and inflammation, major pharmaceutical companies are developing PAK inhibitors as new drugs (ref 10).
Ed Manser currently holds joint appointments with Astar Neuroscience Research Partnership (NRP) and Institute of Medical Biology (IMB).
#ISI is the Institute for Scientific Information (Thomson Scientific)
1. Reubinoff BE, Pera MF, Fong CY, Trounson A, Bongso A. (2000) Embryonic stem cell lines from human blastocysts: somatic differentiation in vitro. Nat Biotechnol. 18: 399-404.
2. Janicke, RU; Sprengart, ML; Wati, MR; Porter, AG (1998) Caspase-3 is required for DNA fragmentation and morphological changes associated with apoptosis. J. Biol Chem. 273: 9357-60.
3. Manser E, Leung T, Salihuddin H, Zhao ZS, Lim L. (1994) A brain serine/threonine protein kinase activated by Cdc42 and Rac1. Nature 367: 40-6.
4. Diekmann D, Brill S, Garrett MD, Totty N, Hsuan J, Monfries C, Hall C, Lim L, Hall A. (1991) Bcr encodes a GTPase-activating protein for p21rac Nature 351: 400-2.
5. Manser E, Leung T, Salihuddin H, Tan L, Lim L (1993) A non-receptor tyrosine kinase that inhibits the GTPase activity of p21cdc42. Nature 363: 364-7.
6. Zhang XF, Settleman J, Kyriakis JM, Takeuchi-Suzuki E, Elledge SJ, Marshall MS, Bruder JT, Rapp UR, Avruch J (1993). Normal and oncogenic p21ras proteins bind to the amino-terminal regulatory domain of c-Raf-1. Nature 364: 308–13.
7. Manser E, Loo TH, Koh CG, Zhao ZS, Chen XQ, Tan L, Tan I, Leung T, Lim L. (1998) PAK kinases are directly coupled to the PIX family of nucleotide exchange factors. Mol Cell. 1:183-92.
8. Zhao ZS, Manser E, Loo TH, Lim L. (2000) Coupling of PAK-interacting exchange factor PIX to GIT1 promotes focal complex disassembly. Mol Cell Biol. 20: 6354-63.
9. Say E, Tay HG, Zhao ZS, Baskaran Y, Li R, Lim L, Manser E. (2010) A functional requirement for PAK1 binding to the KH(2) domain of the fragile X protein-related FXR1. Mol Cell. 38: 236-49.
10. Kichina JV, Goc A, Al-Husein B, Somanath PR, Kandel ES. (2010) PAK1 as a therapeutic target. Expert Opin Ther Targets. 14: 703-25.