Dr. Mirvat El-Sibai's Lab


Systems: Along with working with various cell culture models, we aim to correlate the in vitro effects/fucntions of proteins to their in vivo expression patterns in human tissues taken from patiens. We are in the process of building our database of normal and human tissues by collecting pathology specimen from Clemenceau Medical Center (CMC), Makassed hospital, Hammoud hospital, Clinique Rizk and Rafik Hariri Unversity Hospital (RGUH).

The brain tumor project:

The term brain tumor refers to a group of heterogeneous neoplasms with similar clinical manifestations and diagnostic approaches, but each has its own etiology, treatment, and prognosis. Based on the classification of the World Health Organization (WHO), astrocytomas are assigned into one of four prognostic grades, with grades III and IV considered malignant. While systemic metastasis of malignant astrocytomas rarely occurs, these tumors are highly invasive into adjacent and distant tissues of the normal brain which makes them surgically and medically unmanageable. Cell migration, which ultimately leads to tumor invasion, is a complex process that starts by a series of intracellular signals leading to the dynamic regulation of the cytoskeleton in response to specific environmental cues. We have an extensive background and expertise studying the regulation of cell motility, particularly by Rho GTPase signaling (see figure), leading to tumor metastasis and invasion. 

Rho GAPs are inhibitors of Rho GTPases that have been implicated as tumor suppressors. Recently, Rho GAPs were found to be underexpressed in brain tumors, particularly astrocytomas. Based on that, we want to identify the exact role of Rho GAPs in brain tumor invasion. StarD13, which is also referred to as START-GAP2 or DLC2, was first described as a tumor suppressor gene product and it was found to be underexpressed in hepatocellular carcinoma cells. This Rho-GAP, whose gene is located on the position 13q12.3, specifically inhibits the function of RhoA and Cdc42 and was demonstrated to inhibit, in cultured cells, the Rho-mediated assembly of actin stress fibers. Furthermore, overexpression of StarD13 is associated with a decrease in cell growth. Many following studies confirmed StarD13 to be a potential potent tumor suppressor. The aforementioned clues and our interest in the role of Rho GTPases in tumor invasion and metastasis have led us to develop an interest in investigating the regulation of Rho GTPases through StarD13. Correcting for the lack of this tumor suppressor in many known tumors presents a very powerful potential tool for cancer therapeutics.

We are examining the role of StarD13 in astrocytoma cell lines and examining the expression level of StarD13 across different grades of astrocytoma tissues taken from patients.

Along wih StarD13, we are also examining the expression levels of different metastatic regulators, including RhoGTPases, in grade I-IV astrocytoma tissues from patients by immunohistochemistry and western blot.

 The breast cancer project:

Breast cancer is one of the most commonly diagnosed cancers in women around the world. Invasion and metastasis are the cause of cancer-related death in breast cancer patients. Cell migration, which ultimately leads to tumor invasion, is a complex process that starts by a series of intracellular signals leading to the dynamic regulation of the cytoskeleton in response to specific environmental cues. These processes are mainly regulated by Rho family of small guanosine triphosphatases (GTPases). The three most characterized members of the Rho family are Rho, Rac, and Cdc42.

 We have previously shown that Cdc42 is the main Rho GTPase leading to actin polymerization and protrusion formation in EGF-stimulated rat breast adenocarcinoma cells, MTLn3 cells (El-Sibai et al., 2007). This was shown to be through the activation of the WASP family of proteins and Arp2/3 downstream of Cdc42 and upstream of actin activation (El-Sibai et al., 2007). Recent work confirmed our work in MTLn3 cells, showing Cdc42 to be required for protrusion and motility in melanoma cell lines (Gadea et al., 2008). This has been described specifically for cancer cells and not for macrophages or fibroblasts, where Rac was the Rho GTPase needed for motility (Ridley, 2001; Ridley et al., 1992). We hope that this the answer to differentially inhibit motility in cancer cells without affecting healthy cell motility in normal cells. We have also innovated the role of RhoA in cancer cell lines by proving that RhoA has a function at the leading edge of cancer cells (El-Sibai et al., 2008).

 StarD13 could be exerting its tumor suppressor role through the inhibition of Cdc42 activity. Preliminary data from our laboratory showed that the total level of expression of the Cdc42 protein showed an increase in the more malignant astrocytomas, as compared to the low grade astrocytomas. This could be consistent with an oncogenic pro-invasive role of Cdc42 in malignant astrocytomas. This project investigates the roles of Cdc42, StarD13 as well as Rho in breast cancer.