Current Research Interests and Projects:
Drug addiction is a chronic relapsing disease of the brain manifested by a variety of behaviors that are detrimental to both the individual and society. An understanding of the neurobiology of addiction will require knowledge about how the brain functions normally and how opioid drugs alter brain functioning over the course of addiction. Opioid drugs initiate their effects by engaging opioid receptors on the cell surface of brain cells. The molecular cloning of cDNAs from the three major subtypes of opioid receptors, , and , has opened new avenues to study opioid receptor activation and signal transduction pathways. Although predictions about the general nature of the receptor binding site have been made based on the structures of opioid alkaloids and peptides, the role of particular domains and amino acid residues for proper receptor function has been recently studied using the methodology of in vitro mutagenesis in conjunction with analysis of receptor chimeras. Our research program seeks to identify the critical structural determinants that comprise the surface of the ligand binding crevice for the , and opioid receptors, and to identify the residues that are responsible for the ligand selectivity of these receptor subtypes. In addition, amino acids within the receptor that are responsible for activation of G proteins and agonist-stimulated down regulation are being characterized. This research will have a direct impact on the long-term objective to understand, at the molecular level, how opioid receptors interact with their ligands and activate signal transduction pathways that result in cellular responses. Another area being pursued is regulation of gene expression by acute and chronic morphine treatment. DNA chip technology is being used to screen for genes that are regulated by opioid agonists, and during induction of withdrawal from opioids. It is anticipated that the molecular and cellular studies of the effects of opioid drugs and peptides will aid in the elucidation of the mechanisms involved in tolerance to, and physical dependence on, opioids.

Representative Publications:

Tirumalai, P. and Howells, R. D. Regulation of calbindin-D28k gene expression in
response to acute and chronic morphine administration. Mol. Brain Res. 23, 144-150 (1994).

Wang, W. W. and Howells, R. D. Sequence of the 5'-flanking region of the rat c-fos
proto-oncogene. Gene 143, 261-264 (1994).

Shahrestanifar, M., Saha, D. P., Scala, L. A., Baus, A. and Howells, R. D. Cloning of a
human cDNA encoding a putative nucleotide-binding protein related to Escherichia coli
MinD. Gene 147, 281-285 (1994).

Shahrestanifar, M. and Howells, R. D. Sensitivity of mu and delta opioid receptor
binding to N-ethylmaleimide. Reg. Peptides 54, 269-270 (1994).

Wang, W. W., Shahrestanifar, M., Jin, J. and Howells, R. D. Studies on µ and opioid
receptor selectivity utilizing chimeric and site-mutagenized receptors. Proc. Natl. Acad.
Sci. USA 92, 12436-12440 (1995).

Shahrestanifar, M., Wang, W. W. and Howells, R. D. Studies on inhibition of µ and
opioid receptor binding by dithiothreitol and N-ethylmaleimide: His 223 is critical for µ
opioid receptor binding and inactivation by N-ethylmaleimide. J. Biol. Chem. 271,
5505-5512 (1996).

Shahrestanifar, M. and Howells, R. D. Sensitivity of opioid receptor binding to N-
substituted maleimides and methanethiosulfonate derivatives. Neurochem. Res. 21,
1295-1299 (1996).

Wu, G., Lu, Z. H., Wei, T. J., Howells, R. D., Christoffers, K. H. and Ledeen, R. W. The role of GM1 ganglioside in regulating excitatory opioid function. Annals New York Acad. Sci. 12, 1-13 (1998).

Cai, H., Howells, R.D., and Wagner, B.J. Identification of a novel gene product preferentially expressed in rat lens epithelial cells. Molecular Vision 5, 3 http://www.molvis/v5/p3, 1999.

Chaturvedi, K., Shahrestanifar, M. and Howells, R. D. Mu opioid receptor: role for the amino terminus as a determinant of ligand binding affinity. Mol. Brain Res. 76: 64-72, 2000.

Chaturvedi, K, Jiang, X.., Christoffers, K. H, Chinen, N., Bandari, P., Raveglia, L. F.,Ronzoni, S., .Dondio, G. and Howells, R. D. Pharmacological profiles of selective non-peptidic delta opioid receptor ligands. Mol. Brain Res. 80: 166-176, 2000.

Chinen, N., Wu, G., Dondio, G., and Howells, R. D. Ligand/receptor interactions
revealed by analysis of the pH dependence of binding to mu and delta opioid receptors.
Submitted Mol. Brain Res.

Chaturvedi, K., Bandari, P., Chinen, N., and Howells, R. D. Opioid receptor down-regulation: involvement of the proteasome. Submitted J. Biol. Chem.

Chaturvedi, K., Christoffers, K., Singh, K. and Howells, R.D. Down Regulation of
Opioid Receptors, Biopolymers/Peptide Science, in press, 2000.