Samit Adhya , Ph.D., FNA, FNASc
The Genetic Engineering laboratory of the MHG Division is currently engaged in research on the transport of RNA molecules across mitochondrial membranes. This work has two facets. The first relates to the mechanism of transport; the second to the application of this phenomenon to mitochondrial gene therapy.
Mechanism of mitochondrial tRNA import: tRNAs are imported into mitochondria of Leishmania and other species by an unknown mechanism. An in vitro import system was developed for the first time internationally. The role of RNA sequence in import was elucidated. A novel membrane-associated import factor was described. The energetics of import was studied. A new stepwise import model for import was proposed. Import signals on some tRNAs were identified. Inter-tRNA interactions at the inner membrane were discovered. In 2003, a multiprotein complex (RIC) competent for import was purified. The subunits of the complex were identified by a combination of biochemical and genetic approaches. Currently, the mechanism of tRNA recognition and translocation is being worked out using biochemically defined systems.
RIC is the first and so far the only mitochondrial RNA import machine to be molecularly defined.
“… Mukherjee and colleagues provide a comprehensive description of the isolation and preliminary characterization of the RIC that mediates mitochondrial tRNA import in the kinetoplastid protozoon Leishmania tropica…..a fuller understanding of the tRNA-import process as provided by Mukherjee and colleagues might also have an impact on the rescue of mitochondrial dysfunctions.”, Marc Mirande, EMBO Reports, 2007.
Mitochondrial gene therapy protocol: Mitochondrial dysfunction is known to underlie many human diseases, but is untreatable due to the lack of a suitable gene transformation system. The Adhya group showed that RIC is taken up and targeted to mitochondria of human cells in a biologically active form, inducing import of intracellular tRNAs and correction of the respiratory defect caused by a pathogenic mitochondrial tRNA mutation (Mahata et al., Science, 2006).
This finding has raised international expectations of a new and efficient mitochondrial gene delivery system.
“…Mahata and colleagues investigated whether this complex, RIC (RNA import complex), could be used to restore mitochondrial function in cells from patients with myoclonic epilepsy with ragged red fibres (MERFF) and Kearns–Sayre syndrome (KSS)…. this approach could potentially be used to treat several other diseases that are caused by mitochondrial tRNA mutations. The authors point out that RIC also mediates the translocation of small RNAs, raising the exciting possibility of using this approach for a wider range of conditions by manipulating the expression of mitochondrial genes.” Loisa Flintoft, Nature Reviews Genetics, 2006.
“RIC treatment could combat a variety of severe disorders involving mitochondrial tRNA mutations” Orla Smith, Cell, 2006.
Ongoing work is focused on the use of RIC to deliver small and large functional RNA to mitochondria in cultured cells as well as in vivo. This method depends on the ability of RIC to be taken up by mammalian cells and transported to mitochondria. RIC, or its derivatives, were later shown to deliver short and long RNA sequences, attached to the complex by a signal tag, to mitochondria. While the potential of this method to clinically correct mitochondrial disorders is obvious, the mechanism of uptake, intracellular transport and mitochondrial targeting of the ribonucleoprotein (RNP) remain to be worked out.
Ph.D. (USA), FNA., FNASc
Patents & Publications
- Bhattacharyya, S.N., Chatterjee, S. and Adhya, S. (2002) Mitochondrial RNA import in Leishmania tropica: aptamers homologous to multiple tRNA domains that interact cooperatively or antagonistically at the inner membrane. Mol. Cell. Biol. 22, 4372-4382.
- Bhattacharyya, S.N., Chatterjee, S., Goswami, S., Tripathi, G., Dey, S.N. and Adhya, S. (2003) “Ping-Pong” interactions between mitochondrial tRNA import receptors within a multiprotein complex. Mol. Cell. Biol. 23, 5217-5224.
- Goswami, S., Chatterjee, S., Bhattacharyya, S. N., Basu, S. and Adhya, S. (2003) Allosteric regulation of tRNA import: interactions between tRNA domains at the inner membrane of leishmania mitochondria. Nucl. Acids Res. 31, 5552-5559.
- Ghosh, S., Goswami, S. and Adhya, S. (2003) Role of superoxide dismutase in survival of Leishmania within the macrophage. Biochem. J. 369, 447-452.
- Adhya, S., Basu, S., Bhattacharyya, S.N., Chatterjee, S., Dhar, G., Goswami, S., Ghosh, S., Home, P., Mahata, B. and Tripathi, G. (2003) Mitochondrial differentiation in kinetoplastid protozoa: A plethora of RNA controls. Differentiation 71, 549-556.
- Bhattacharyya, S.N. and Adhya, S. (2004) tRNA-triggered ATP hydrolysis and generation of membrane potential by the Leishmania mitochondrial tRNA import complex. J. Biol. Chem. 279, 11259-11263.
- Bhattacharyya, S.N. and Adhya, S. (2004) The complexity of mitochondrial tRNA import. RNA Bio. 1, 84-88.
- Mahata, B., Bhattacharyya, S.N., Mukherjee, S. and Adhya, S. (2005) Correction of translational defects in patient-derived mutant mitochondria by complex-mediated import of a cytoplasmic tRNA. J. Biol. Chem. 280, 5141-5144.
- Goswami, S., Dhar, G., Mukherjee, S., Mahata, B., Chatterjee, S., Home, P. and Adhya, S. (2006) A bi-functional tRNA import receptor from Leishmania mitochondria Proc. Natl. Acad. Sci. USA, 103, 8354-8359.
- Goswami, S. and Adhya, S. (2006) The a subunit of Leishmania F1 ATP synthase hydrolyzes ATP in presence of tRNA. J. Biol. Chem. 281, 18914-18917.
- Chatterjee, S., Home, P., Mukherjee, S., Mahata, B., Goswami, S., Dhar, G. and Adhya, S. (2006) An RNA-binding respiratory component mediates import of type II tRNAs into Leishmania mitochondria. J. Biol. Chem. 281, 25270-25277.
- Mahata, B., Mukherjee, S., Mishra, S., Bandyopadhyay, A. and Adhya, S. (2006) Functional delivery of a cytosolic tRNA into mutant mitochondria of human cells. Science 314, 471-474.
- Mukherjee, S., Basu, S., Home, P., Dhar, G., and Adhya, S. (2007). Necessary and sufficient factors for import of tRNA into the kinetoplast-mitochondrion. EMBO Rep. 8, 589-595.
- Basu, S., Mukherjee, S. and Adhya, S. (2008) Proton-guided movements of tRNA within the Leishmania mitochondrial RNA import complex. Nucl. Acids Res. 36, 1599-1609.
- Mukherjee, S., Mahata, B., Mahato, B. and Adhya, S. (2008) Targeted mRNA degradation by complex-mediated delivery of antisense RNAs to intracellular human mitochondria. Hum. MolecGenet 17, 1292-1298.
- Home, P., Mukherjee, S., and Adhya, S. (2008)A mosaic of RNA binding and protein interaction motifs in a bifunctional mitochondrial tRNA import factor from Leishmania tropica Nucl. Acids Res. 36, 5552-5561.
- Adhya, S. (2008) Leishmania mitochondrial tRNA importers. Int. J. Biochem. Cell Biol. 40, 2681-2685.
- Mahato, B, Jash, S., Adhya, S., (2011). RNA-mediated restoration of mitochondrial function in cells harboring a Kearns Sayre Syndrome mutation. Mitochondrion 11, 564-574.
- Jash, S., Adhya, S., (2011). Suppression of reactive oxygen species in cells with multiple mitochondrial DNA deletions by exogenous protein-coding RNAs. Mitochondrion, 11, 607-614.
- Adhya, S., Mahato, B., Jash, S., Koley, S., Dhar, G. and Chowdhury, T. (2011). Mitochondrial gene therapy: The tortuous path from bench to bedside. Mitochondrion 11, 839-844.