Research in the Krishnamurthy lab focuses on host response during viral infections.
Our studies address the fundamental mechanisms by which cells resist infection and
how cells know they are infected by a virus. The innate immune pathway is the first
line of defense against viruses and functions to limit viral replication and spread.
Pattern-Recognition Receptors including Rig-I-like helicases (Rig-I and MDA5) and
Toll-like receptors (TLRs) recognize conserved microbial features (Pathogen associated
Molecular Pattern, PAMP) and provide signals to initiate immune response by producing
type I IFN and cytokines. Double stranded RNA produced during viral infections serves
as PAMP and activates the IFN-inducible 2’,5’ - oligoadenylate synthetase (OAS) which
converts cellular ATP to unique 2’,5’ - linked oligoadenylates, 2-5A, which binds
and activates a ubiquitous and latent endoribonuclease, RNase L. Activated RNase L
cleaves single stranded viral and host RNAs to produce small RNAs with duplex structures
which can signal through Rig-I and MDA5 to amplify the production of IFNb. Studies
in the lab are aimed at investigating the signaling pathway initiated by small RNA
cleavage products of RNase L and the expanding roles of RNase L in innate immunity.
Areas of research in our group include:
Regulation of autophagy and cell death pathways: We have shown recently that activation of RNase L induces autophagy involving the activities of dsRNA-dependent protein kinase R (PKR) and c-jun N-terminal kinase (JNK). The regulation of autophagy and innate immunity to viral infections appears to involve overlapping signaling pathways and autophagy-related proteins can have both proviral and antiviral effects. It is not clear how these two pathways interact and how the activation of one might complicate the outcome of the other, i.e., could the induction of autophagy modulate innate immune responses to viral infection? Ongoing studies are determining the role of RNA signaling pathways in the crosstalk between autophagy and apoptosis during viral infections.
Non-enzymatic antiviral role of RNase L: Our recent studies identified a novel interaction between the antiviral endoribonuclease RNase L and the actin binding protein Filamin A that enhances host defense by preventing viral entry into naive cells. This role for RNase L is independent of its enzymatic function. Virus infection alters actin dynamics, disrupts the RNase L-Filamin A complex and releases RNase L to mediate antiviral signaling and effector functions via its established nucleolytic activities. Current studies are aimed at determining the impact of altered actin dynamics and cytoskeletal proteins in regulating virus trafficking in polarized and non-polarized models of infection.
Role of small cellular RNAs generated by RNaseL in innate immunity: Previous studies showed that activity of RNase L on cellular RNA generates small self-RNAs that activate Rig-I and MDA5, producing IFN-β through activation of the IRF3 transcription factor. Cloning and characterization of various host small RNAs will allow us to establish the features of RNAs that are needed to activate Rig-I or MDA5 and the basis of discrimination of “self” and “nonself”. The identification of small RNAs with ability to induce IFN-β and or modulate inflammatory responses would be a critical early step in the development of antiviral and antitumor therapies with improved outcomes.
RNase L-Filamin A interaction in prostate cancer: We have identified a novel interaction of RNase L with actin-binding protein, Filamin A. Interaction of Filamin A with AR inhibits transcriptional activity of AR. Previous studies have shown that RNase L interacts with AR, and the interaction is stimulated by androgens. Also, mutations in RNASEL correlate with incidence of hereditary prostate cancer. In light of these correlations, we are investigating the role of RNase L in prostate cancer.
RNase L cleavage products promote switch from autophagy to apoptosis by caspase-mediated cleavage of Beclin-1. Siddiqui, MA, Mukherhee, S, Manivannan, P and Malathi K* Int. J. Mol. Sci. 2015, 16, 17611-17636; doi:10.3390/ijms160817611. (*Communicating author).
RNase L Interacts with Filamin A To Regulate Actin Dynamics and Barrier Function for
Viral Entry. Malathi K*, Siddiqui MA, Dayal S, Naji M, Ezelle HJ, Zeng C, Zhou A, Hassel BA. MBio. 2014 Oct
28;5(6). pii: e02012-14. doi: 10.1128/mBio.02012-14 (* communicating author).
RNase L contributes to experimentally induced type 1 diabetes onset in mice. Zeng C, Yi X, Zipris D, Liu H, Zhang L, Zheng Q, Malathi K, Jin G, Zhou A. J Endocrinol. 2014 Dec;223(3):277-87. doi: 10.1530/JOE-14-0509. Epub 2014 Oct 6.
Epigallocatechin-3-gallate suppresses proinflammatory cytokines and chemokines induced by Toll-like receptor 9 agonists in prostate cancer cells. Mukherjee S, Siddiqui MA, Dayal S, Ayoub YZ, Malathi K*. J Inflamm Res. Jun 17;7:89-101, 2014. (*Communicating author).
Siddiqui MA, Malathi K*. RNase L induces autophagy via c-Jun N-terminal kinase and double-stranded RNA-dependent protein kinase signaling pathways. J Biol Chem. 2012 Dec 21;287(52):43651-64. (*Communicating author).
Malathi K, Saito T, Crochet N, Barton DJ, Gale M Jr, Silverman RH. RNase L releases a small RNA from HCV RNA that refolds into a potent PAMP. RNA. Nov;16(11):2108-19, 2010.
Malathi K, Dong B, Gale M and Silverman RH. Small self RNA generated by RNase L amplifies Antiviral Innate Immunity. Nature. Aug 16;448(7155):816-9, 2007.
Dong B, Kim S, Hong S, Das Gupta J, Malathi K, Klein EA, Ganem D, Derisi JL, Chow SA, Silverman RH. From the Cover: An infectious retrovirus susceptible to an IFN antiviral pathway from human prostate tumors. Proc. Natl. Acad. Sci. U.S.A, Jan 30;104(5):1655-60, 2007.
Molinaro RJ, Jha BK, Malathi K, Varambally S, Chinnaiyan AM, Silverman RH. Selection and cloning of poly(rC)-binding protein 2 and Raf kinase inhibitor protein RNA activators of 2',5'-oligoadenylate synthetase from prostate cancer cells. Nucleic Acids Res. 34(22):6684-95, 2006.
Malathi, K., Paranjape, J.M., Bulanova, E., Shim, M., Guenther-Johnson, J.M., Faber, P.W., Eling, T.E., Williams, B.R.G., and Silverman, R.H. A novel transcriptional signaling pathway in the interferon system mediated by 2'-5'-oligoadenylate activation of RNase L. Proc. Natl. Acad. Sci. U.S.A., 102, 14533-14538, 2005.
Zhou, A., Molinaro, R.J., Malathi, K., and Silverman, R.H. Mapping of the human RNASEL promoter and expression in cancer and normal cells. J. Interferon & Cyt. Res., 25, 595-603, 2005.
Malathi K, Li X, Krizanova O, Ondrias K, Sperber K, Ablamunits V, Jayaraman T. Cdc2/cyclin B1 interacts with and modulates inositol 1,4,5-trisphosphate receptor (type 1) functions. J Immunol. 2005 Nov 1;175(9):6205-10.
Malathi K, Paranjape JM, Ganapathi R, Silverman RH. HPC1/RNASEL mediates apoptosis of prostate cancer cells treated with 2',5'-oligoadenylates, topoisomerase I inhibitors, and tumor necrosis factor-related apoptosis-inducing ligand. Cancer Res. 2004 Dec 15;64(24):9144-51.
Tantral, L., Malathi, K., Kohyama, S., Silane, M., Berenstein, A., and Jayaraman, T. Intracellular calcium release is required for caspase-3 and –9 activation. Cell Biochem. and Function. 22(1): 35-40. 2004.
Malathi, K., Higaki, K., Tinkelenberg, A.H., Balderes, D.A., Almanzar, D., Wilcox, L., Erdeniz, N., Redican, F., Padamsee, M, Liu, Y., Khan, S., Alcantara, F., Carstea, E.D., Morris, J.A., and Sturley, S.L. Mutagenesis of the putative sterol sensing domain of the yeast Niemann Pick C related protein reveals a primordial role in subcellular sphingolipid distribution. J Cell Biol.164(4):547-56. 2004
Editorial on the above paper ` A primordial mover of sphingolipids’ in J. Cell Biol. 164(4): 476, 2004.
Malathi, K., Kohyama, S., Ho, M., Soghoian, D., Li, X., Silane, M., Berenstein, A., and Jayaraman, T. Inositol 1,4,5-triphosphate receptor (type 1) phosphorylation and modulation by cdc2. J. Cell. Biochem.90(6): 1186-96, 2003.
Malathi,K., Xiao, Y., and Mitchell, A.P. Catalytic roles of yeast GSK3beta/shaggy homolog Rim11p in meiotic activation. Genetics. 153:1145-1152. 1999.
Malathi,K., Xiao, Y., and Mitchell.A.P. Interaction of yeast repressor-activator protein Ume6p with glycogen synthase kinase 3 homolg Rim11p. Mol. Cell. Biol. 17(12): 7230-7236. 1997.
Malathi, K., Ganesan , K.,and Datta, A. Identification of a putative transcription factor in C.albicans that can complement the mating defect of S.cerevisiae ste12 mutants. J. Biol. Chem. 269: 22945-51. 1994.
Singh,P., Ganesan, K. , Malathi,K., Ghosh, D., and Datta, A. ACPR, a STE12 homologue from C.albicans, is a strong inducer of pseudohyphae in S.cerevisiae haploids and diploids. Biochem. Biophys. Res. Comm. 205 (2) 1079-85. 1994.
Mohammad Adnan Siddiqui
Undergraduate students (present to past)
George Karwe Chalupe (OSU)
Arianne Lovey Sky
Jamie Marie Spencer