The Laboratory of Receptor Biology

The lab of Receptor Biology explores novel roles of G protein coupled receptors (GPCRs) in regulation of protein degradation. Specifically we use biochemical and molecular biology tools to study GPCR-mediated degradation of the pro-inflammatory enzyme COX-2  via pathways that do not involve classical GPCR signaling but rather facilitate COX-2 ubiquitination and degradation in the proteasome. 

The cyclooxygenase (COX) enzyme isoforms COX-1 and COX-2 catalyze the rate-limiting step in the conversion of arachidonic acid (AA) to prostaglandins- bioactive lipids that play central roles in cardiovascular, immunological and brain function. As opposed to COX-1, which is expressed at constitutive levels in most tissues, COX-2 undergoes a process of rapid upregulation in response to a wide range of inflammatory and pathological signals and many epidemiologic studies show that overexpression of COX-2 is a prominent feature of pre-malignant and malignant neoplams. Despite the existence of effective non steroidal anti-inflammatory drugs (NSAIDs) that inhibit COX activity accumulating evidence show that COX-2 has additional non-enzymatic roles, and that disease with elevated COX-2 may be treated by reducing COX-2 levels

 

Our lab is interested in the mechanisms and proteins that regulate COX-2 degradation, with a special focus on GPCR-mediated pathways. 
 
We combine in vitro and in vivo approaches to:

Identify the specific ubiquitination "barcodes" that determine the place and rate of COX-2 degradation, and the proteins that interact with these specific sites. We propose that the changes in the conformation of COX-2 (e.g. following substrate binding) expose different sites of ubiquitination that in turn determine the place and magnitude of protein degradation. We therefore study the ubiquitination of COX-2 under quiescent, substrate-activated, and inhibited conditions, establish which of the lysines is involved in the process, and reveal identity of the involved E3 ligases
 
Understand the novel role of G protein-coupled receptors (GPCRs) in the degradation of COX-2. Our recent work has shown that several GPCRs (e.g. EP1, β1AR, AT1) downregulate COX-2 expression by facilitating its degradation via the proteasome. We are currently focusing on identifying. Importantly, the effect of GPCRs on COX-2 does not require any activation of the receptor, thus suggesting a new role for GPCRs as scaffold proteins that may be involved in regulation of protein expression. We are therefore studying the effect of different GPCRs on COX-2 ubiquitination and degradation; identify which E3 ligases are involved in GPCR-mediated ubiquitination of COX-2; testing whether receptor-mediated ubiquitination of COX-2 is mediated by the accessory proteins and the role of ubiquitination sites on GPCRs in downregulating COX-2 expression. Based on the results of these studies we aim to design small peptides that accelerate COX-2 degradation as a possible novel therapeutic target of COX-2
 
Study Changes in COX-2 degradation under pathological conditions. 
 In a collaborative study with Prof. Gal Richter Levin we showed that a near drowning experience causes an emotional response one month after trauma infliction. Biochemically, COX-2 levels were elevated only in the ventral CA1 area of the hippocampus with a concomitant reduction in its ubiquitination levels. We are currently elucidating the role of COX-2 degradation in diseases such as PTSD and under several treatment regimes 
 
Unraveling the pathways and mechanisms that control COX-2 expression and stability through its degradation may well underpin development of novel therapeutic approaches designed to modulate COX-2 protein . In terms of GPCR biology, we point to a novel unexpected role for GPCRs in regulation of COX-2 protein degradation by non canonical pathways. Deciphering these mechanisms is critical because GPCRs are involved in almost every aspect of human disease, and their levels are significantly altered in the course of many diseases (e.g. heart failure, asthma, Alzheimer's disease). Designing short peptides that are based on GPCR sequences to downregulate COX-2 expression offers a novel target of pharmaceutical intervention that may be of great significanct