Jairaj K. Acharya, MBBS, Ph.D.

Senior Investigator

Cancer and Developmental Biology Laboratory

NCI/CCR

Building 560, Room 22-6
Frederick, MD 21702-1201

301-846-7051

acharyaj@mail.nih.gov

Research Topics

Phospholipid Signaling

Our long-term objective is to understand the complex interrelationship between phospholipid and sphingolipid metabolism and metabolic signaling in vivo. Intermediates of phospholipid (PL) and sphingolipid (SL) metabolism serve as second messengers for a number of signaling cascades including activation of G-protein-coupled receptors such as adrenaline and thrombin as well as receptor tyrosine kinases by growth factors. They mediate a number of processes ranging from protein secretion to activation of apoptosis. We have initiated studies to understand several aspects of lipid signaling in Drosophila.

Lipid Reservoirs and Signaling. Sphingomyelin (or phosphorylethanolamine ceramide, CPE, in flies) could serve as a reservoir for several lipid messengers such as ceramide, ceramide 1-phosphate, sphingosine, and sphingosine 1-phosphate. We have initiated studies to delineate the in vivo role of some of the enzymes of the putative "Sphingomyelin Cycle". We have begun by identifying homologous genes in Drosophila. We are using transgenic gain of function and mutagenic loss of function studies to analyze the importance of such a pathway in Drosophila. We have recently demonstrated that modulation of the sphingolipid biosynthetic pathway such as targeted expression of ceramidase, rescues degeneration in certain photoreceptor mutants. We have also demonstrated that ceramidase facilitates membrane turnover and rhodopsin endocytosis in Drosophila photoreceptors.

Sphingolipids are synthesized vectorially. While the steps that lead up to the generation of ceramide occurs in the endoplasmic reticulum (ER) the biosynthesis of sphingomyelin(or CPE) and most complex sphingolipids occurs outside of the ER, either in the Golgi Complex or in the plasma membrane. This necessitates the active transport of ceramide from ER to the Golgi Complex. The transport is largely mediated by a protein called ceramide transfer protein (CERT). We have now demonstrated that CERT-mediated transfer of ceramide is critical for the biosynthesis of sphingomyelin (or CPE in Drosophila) and complex sphingolipids. Lack of CERT in Drosophila leads to decreased CPE and they have plasma membranes with altered physical and physiological properties. The changes render them susceptible to normal loads of reactive oxygen species encountered in a cell. The ensuing oxidative damage of plasma membrane leads to production of lipid peroxides that will further oxidize membrane and cellular constituents leading to a rapid deterioration in the metabolic function of cell. The underlying pathoglogic changes manifest as accelerated aging in these mutant flies and consequently they have a short adult life span.

Lipid Distribution and Signaling. PL and SL at the plasma membrane play an important role in stimulus-response coupling, cell differentiation, movement, and exo- and endocytosis. They are asymmetrically distributed in biological membranes and different proteins catalyzing uni- and bidirectional movements of lipids perpetuate asymmetry. Our initial studies involving the generation and characterization of mutants of scramblases in Drosophila indicate a modulatory role for these proteins in regulated exocytosis and no determining role in scrambling of phospholipids. This has implications in a wide range of cellular processes. Further studies should enable us to dissect its role further.

Biography

Dr. Jairaj Acharya obtained his M.B.B.S. from the University of Gulbarga (Government Medical College, Bellary), India, in 1985 and received his Ph.D. in biochemistry from the Indian Institute of Science, Bangalore, in 1993 under Prof. Appaji Rao. He joined Dr. Charles Zuker at the University of California, San Diego as an associate of the Howard Hughes Medical Institute for his postdoctoral training. He was recruited by the NCI in 1999.

Selected Publications

  1. Kosakowska-Cholody T, Lin J, Srideshikan SM, Scheffer L, Tarasova NI, Acharya JK. HKH40A downregulates GRP78/BiP expression in cancer cells. Cell Death Dis. 2014;5:e1240.

  2. Rao RP, Scheffer L, Srideshikan SM, Parthibane V, Kosakowska-Cholody T, Masood MA, Nagashima K, Gudla P, Lockett S, Acharya U, Acharya JK. Ceramide transfer protein deficiency compromises organelle function and leads to senescence in primary cells. PLoS One. 2014;9(3):e92142.

  3. Rahman M, Nirala NK, Singh A, Zhu LJ, Taguchi K, Bamba T, Fukusaki E, Shaw LM, Lambright DG, Acharya JK, Acharya UR. Drosophila Sirt2/mammalian SIRT3 deacetylates ATP synthase β and regulates complex V activity. J Cell Biol. 2014;206(2):289-305.

  4. Kunduri G, Yuan C, Parthibane V, Nyswaner KM, Kanwar R, Nagashima K, Britt SG, Mehta N, Kotu V, Porterfield M, Tiemeyer M, Dolph PJ, Acharya U, Acharya JK. Phosphatidic acid phospholipase A1 mediates ER-Golgi transit of a family of G protein-coupled receptors. J Cell Biol. 2014;206(1):79-95.

  5. Masood MA, Rao RP, Acharya JK, Blonder J, Veenstra TD. Quantitation of multiple sphingolipid classes using normal and reversed-phase LC-ESI-MS/MS: comparative profiling of two cell lines. Lipids. 2012;47(2):209-26.


This page was last updated on October 3rd, 2018