Dr. Amitabha Mukhopadhyay

The scientific contributions of my research are primarily in the area of cell biology with special emphasis on the regulation of intracellular trafficking. We have addressed fundamental issues in host pathogens interactions with an aim to develop a potentially new therapeutic target for their intervention. Our work has provided important insights into the molecular mechanisms of how intracellular pathogens modulate intracellular trafficking pathways to survive in phagocytes. We have demonstrated using an elegant in vitro reconstitution of transport assay that live Salmonella produce a protein, SopE, that helps recruit Rab5 and NSF on the phagosomes containing live bacteria. This promotes fusion of live Salmonella-containing phagosomes with early endosomes so that lysosomal targeting of such phagosomes is avoided. Thus, it is emerging from these studies that SopE could be a new and specific target for selective elimination of Salmonella from the host cells either by blocking the interaction of SopE with Rab5 or by modulating the content of endocytic GTPases in the host cells to divert trafficking of Salmonella to the lysosomes. Finally, we have tested these hypothesis and shown that it is possible to divert Salmonella to the lysosomes for selective killing by modulating the content of endocytic GTPases in the host cells. Interestingly, we have also shown how Salmonella recruits Lysosome Associated Membrane Protein (LAMP1) by fusing with Golgi derieved LAMP1-containing vesicle through the interaction  of their effector molecule, SipC with host Syntaxin6. This is first evidence how an intracellular pathogen recruits LAMP without their targeting to the lysosomes.

Our discovery of a new receptor system mediating uptake and intracellular degradation of hemoglobin by Leishmania suggests how, lacking heme biosynthetic ability, this parasite might meet the requirement of heme essential for its growth. Interestingly, further characterization of the receptor demonstrated that hemoglobin receptor in Leishmania is a suface localized hexokinase, a well characterized glycolytic enzyme. Recently, we have characterized the intercellular route of hemoglobin and their regulation in the parasites by different Rab GTPases by some elegant novel experiments. Our studies have revealed that signaling from the cytoplasmic tail of the hemoglobin receptor targets the hemoglobin to late degradative compartment suggesting that parasites has devised an unique procedure to target the internalized hemoglobin for degradation in late compartment to generate intracellular heme, essentially required by the parasites for growth. Discovery of this new receptor system  for acquiring heme by Leishmania is significant not only as a notable contribution to biology of this group of intracellular parasites but also as a potential new target against these parasites of paramount public health importance in the developing countries.

Survival of intracellular pathogens in the host cells depends on the balance between pro-inflammatory and anti-inflammatory cytokines suggesting that these cytokines possibly modulate distinct steps in the endocytic pathway and thereby regulate phagosome maturation. However, how cytokine modulate intracellular trafficking is not yet known. We have identified a novel mechanism of cytokine mediated modulation of the expression of Rab GTPase. We have shown that treatment of macrophages with IL-6 specifically induce the expression of Rab5 through the activation of extracellular signal-regulated kinase, whereas IL-12 exclusively unregulate the expression of Rab7 through the activation of p38 MAPK.  Finally, we have shown that IL-12 mediated overexpression of  Rab7 induces lysosomal transport whereas IL-6 stimulates the fusion between early compartments in macrophages and accordingly modulate trafficking and survival of intracellular pathogens in macrophages. This is the first demonstration showing that the existence of a unique regulation of membrane trafficking directly dependent on different cytokines.

We have also made seminal contributions to establish for the first time the feasibility of receptor-mediated enodocytosis as an alternative approach to deliver various drugs to macrophages using exquisite specificity and high efficiency process of scavenger receptor mediated endocytosis. We have shown that scavenger receptor-mediated intracellular delivery of various drugs to macrophages combat various infections as well as cancer cells both in vitro and in vivo.

Awards:
• Young Scientist Award in Biological Sciences, CSIR, Govt. of India, 1991
• Long Term Overseas Research Associateship Award from Department of Biotechnology, Govt. of India, 1993
• National Bioscience Award, Department of Biotechnology, Govt. of India, 2000
• Shanti Swarup Bhatnagar Award, Council of scientific & Industrial Research, Govt. of India, 2002
• Dr. Narayana Rao Oration Award, Indian Council of Medical Research, Govt. of India, 2002
• Ranbaxy Research Award in the field of "Medical Sciences - Basic Research", 2004
• Short Term Overseas Research Associateship Award from Department of Biotechnology, Govt. of India, 2005
• J.C. Bose National Fellow,Department of science & Technology, Govt. of India, 2010
• Fellow of The National Academy of Sciences (FNASc)
• Fellow of Indian National Science Academy (FNA)
• Fellow of Indian Academy of Sciences (FASc)
• Fellow of West Bengal Academy of science & Technology
• Member, Guha Research Conference
• Member, Indian Immunology Society
• Member, Association of Microbiologists of India
• Member, Molecular Immunology Forum (MIF)
• Member: Indian Society of Cell Biology