Anning Lin, Ph.D.

Mechanisms and Regulation of Protein Kinase-mediated Signal Transduction in Inflammation, Apoptosis, and Neoplastic Transformation

Research Summary

The work in my laboratory is focused on cell signal transduction, using a variety of molecular, cellular and genetic strategies. We are interested in understanding how signals of extracellular stimuli or oncogenes are transmitted into mammalian cells, resulting in changes patterns of gene expression and ultimately leading to cell growth, programmed cell death (apoptosis) or malignant transformation.

The cellular signaling network is composed of many signaling pathways that transmit signals from the cell membrane to the nucleus. Two signaling pathways have been chosen as model systems to investigate the mechanisms of signal transduction. The first signaling pathway is the JNK (c-Jun N-terminal protein kinase) pathway. JNK is a member of the mitogen-activated protein kinase (MAP kinase) family and mediates signals from a variety of extracellular stimuli such as growth factors, cytokines, tumor promoters, radiation, and oncogenes like Ras, small G proteins Rac/CDC42Hs, Src, Sis, and Met. Once activated, JNK activates a number of transcription factors, including c-Jun, ATP-2, and Elk that play a critical role in controlling expression of genes involved in many fundamental cellular processes, such as growth, differentiation, apoptosis and transformation. The work from several laboratories, including our research group, has led to identification and cloning of various components of the JNK pathway. However, the precise role of the JNK pathway in many cellular events are still poorly understood, due to the lack of specific chemical inhibitors and constitutively active components of the pathway. Recently, we have fused the specific JNK activating kinase JNKK2 with its target JNK1 and found that the fusion protein functions as a constitutively active Jun kinase which is able to stimulate c-Jun transcription in the absence of any stimuli. This JNKK2-JNK1 fusion protein, along with the dominant negative mutants of JNKK we previously generated, will allow us to directly determine the role of the JNK pathway in various cellular events, such as apoptosis or transformation.

The second signaling pathway that we have been working on is the IKK (IkB kinase) pathway. IKK is the key kinase that controls activation of the transcription factor NF-kB by various stimuli including inflammatory cytokines, viral and bacterial infection and tumor promoters. Once activated, IKK phosphorylates IkB, the cytoplasmic inhibitors of NF-kB, triggering IkB ubiquitination and its subsequent degradation by proteasomes. This allows NF-kB to translocate to the nucleus where it stimulates expression of numerous genes involved in immune response, viral infection and programmed cell death. We have shown that MEKK1, the MAP kinase kinase kinase of the JNK pathway, is also an upstream kinase of IKK. Interestingly, we found that MEKK1 and another IKK upstream kinase NIK regulate IKK activity in a cooperation manner, a potential mechanism that allows IKK be activated by variety of extracellular stimuli. Furthermore, we have recently found that pX, the transcription activator of Hepatitis B virus, was able to stimulate NF-kB activity without activating IKK, suggesting the existence of an alternative mechanism for NF-kB activation.

Finally, we are trying to understand the impact of dysregulation of signal transduction on fundamental cellular processes. To study cell growth, we have chosen myocyte hypertrophy as a model system. Our work demonstrated that activation of different MAP kinases have opposite effect on myocyte hypertrophy. Recently, we found that activation of IKK may also be involved in regulating myocyte growth. To study programmed cell death, we have chosen immune system as a model system. We found that activation of JNK may protect cell from apoptosis. To study cell transformation, we have chosen prostate and breast cancer cells as model systems. We found that dysregulation of JNK and IKK may affect the sensitivity of tumor cells to apoptosis. We believe that investigation of the mechanisms of signal transduction and the role played by specific signaling pathways should provide potential therapeutic targets for prevention and treatment of diseases and cancer.

Selected Papers

Lin A, Frost J, Deng T, Smeal T, Al-Alawi N, Kikkawa U, Hunter T, Brenner A, and Karin M. (1992). Casein kinase II is a negative regulator of c-Jun DNA binding and AP-1 activity. Cell 70:777-789.

Hibi M, Lin A, Smeal T, Minden A, and Karin M. (1993). Identification of an oncoprotein- and UV-responsive protein kinase that binds and potentiates the c-Jun activation domain. Gen. & Dev. 7:2135-2148.

Minden A, Lin A, McMahon M, Lange-Carter, C, Derifard B, Davis R, Johnson G, and Karin M. (1994). Bifurcation in Ras signaling: Raf-1 and MEKK-1 differentially activate ERK and JNK MAP kinases. Science 256:1719-1723.

Lin A, Minden A, Martinetto H, Claret FX, Lange-Carter C, Mercurio F, Johnson GL, and Karin M. (1995). Identification of a dual specificity kinase that activates the Jun kinases and p38-Mpk2. Science 268:286-290.

Minden A, Lin A, Claret FX, Abo A, and Karin M. (1995). Selective activation of the JNK signaling cascade and c-Jun transcriptional activity by the small GTPases Rac and Cde42Hs. Cell 81:1147-1157.

Lu X, Nemoto S, Lin A*. (1997). Identification of c-Jun NH2-terminal protein kinase (JNK)-activating kinase 2 as an activator of JNK but not p38. J. Biol. Chem. (Communication) 272 :24751-24754.

Nemoto S, Xiang J, Huang S, and Lin A*. (1998). Induction of apoptosis by SB202190 through inhibition of p38b mitogen-activated protein kinase. J. Biol. Chem. 273:16415-16420.

Nemoto S, Sheng Z, and Lin A*. (1998). Opposing effects of JNK and p38 MAP kinases on cardiomyocyte hypertrophy. Mol. Cell. Biol. 18:3518-3526.

Nemoto S, DiDonato J A, and Lin A*. (1998). Coordinate regulation of I B kinase by MEKK1 and NIK. Mol. Cell. Biol. 18:7336-7343.

Zheng C, Xiang J, Hunter T, and Lin A*. (1999). Generation of a constitutively active c-Jun N-terminal protein kinase that stimulates c-Jun transcription activity. J. Biol. Chem. 274:28966-28971.

Purcell NH, Chenfei Yu C, He D, Xiang J, Paran N, DiDonato JA, Yamaoka S, Shaul Y, and Lin A*. (2001). Activation of NF- B by hepatitis B virus X protein through an I B kinase-independent mechanism. Am. J. Physiol. 280:G669-677.

Purcell NH, Tang G, Yu C, Mercurio F, DiDonato JA, and Lin A*. (2001). Activation of NF- B is required for hypertrophic growth of primary rat neonatal ventricular cardiomyocytes. Proc. Natl. Acad. Sci. USA 98:6668-6673.

Tang G, Yang J, Minemoto Y, and Lin A*. (2001). Blocking caspase-3-mediated proteolysis of IKKb suppresses TNF-a-induced apoptosis. Molecular Cell 8:1005-1016.

Tang G, Minemoto Y, Dibling B, Purcell NH, Li Z, Karin M, and Lin A*. (2001). Inhibition of JNK activation by NF-kB target genes. Nature 414:313-317. (News and Views, 414:265-266 2001).

Karin M and Lin A. (2002). NF-kB at the crossroad of life and death. Nature Immunology 3:221-227.