Ghada S. Hassan

Loss of Caveolin-1 causes the hyper-proliferation of intestinal crypt stem cells with increased sensitivity to whole body γ-radiation

Caveolin-1 (Cav-1) is a protein marker for caveolae organelles, and acts as a scaffolding protein to negatively regulate the activity of signaling molecules by binding to and releasing them in a timely fashion. We have previously shown that loss of Cav-1 promotes the proliferation of mouse embryo fibroblasts (MEFs) in vitro. Here, to investigate the in vivo relevance of these findings, we evaluated the turnover rates of small intestine crypt stem cells from WT and Cav-1 deficient mice. Interestingly, we show that Cav-1 null crypt stem cells display higher proliferation rates, as judged by BrdU and PCNA staining. In addition, we show that Wnt/?-catenin signaling, which normally controls intestinal stem cell self-renewal, is up-regulated in Cav-1 deficient crypt stem cells. Because the small intestine constitutes one of the main targets of radiation, we next evaluated the role of Cav-1 in radiation-induced damage. Interestingly, after exposure to 15 Gy of ?-radiation, Cav-1 deficient mice displayed a decreased survival rate, as compared to WT mice. Our results show that after radiation treatment, Cav-1 null crypt stem cells of the small intestine exhibit far more apoptosis and accelerated proliferation, leading to a faster depletion of crypts and villi. As a consequence, six days after radiation treatment, Cav-1 -/- mice lost all their crypt and villus structures, while WT mice still showed some crypts and intact villi. In summary, we show that ablation of Cav-1 gene expression induces an abnormal amplification of crypt stem cells, resulting in increased susceptibility to ?-radiation. Thus, our studies provide the first evidence that Cav-1 normally regulates the proliferation of intestinal stem cells in vivo.

Caveolae and Caveolin-1: Novel Potential Targets for the Treatment of Cardiovascular Disease

Caveolae are 50-100 nm cell surface plasma membrane invaginations that are highly enriched in cholesterol and sphingolipids and are characterized by the protein marker caveolin-1. Caveolin-1 is highly expressed in terminally differentiated cells. Among these cells, endothelial cells, smooth muscle cells, and macrophages have all been shown to play key roles in the development of vascular disease. Atherosclerosis and neointimal formation are two major processes that have been associated with arterial occlusion. In both cases, caveolin-1 has been shown to play an important role. However, depending on the cell type and the metabolic pathways regulated by this protein, caveolin-1 may positively or negatively influence the development of vascular disease. Both of these aspects will be discussed in this review.

Caveolin-1 is Required for the Upregulation of Fatty Acid Synthase (FASN), a Tumor Promoter, During Prostate Cancer Progression

Prostate cancer is the second leading cause of cancer-related deaths in men. Fatty acid synthase (FASN) is normally upregulated during human prostate cancer onset and metastatic progression and its expression positively correlates with the development of advanced metastatic disease. However, it remains unknown what molecular factor(s) control FASN expression. It has been hypothesized that FASN functions as a tumor promoter during prostate cancer progression in humans. Consistently, an established mouse of model of prostate cancer, termed TRAMP mice, also shows the progressive upregulation of FASN levels during prostate cancer development. Here, we examine the role of caveolin-1 (Cav-1) in regulating FASN expression during prostate cancer progression. For this purpose, we crossed Cav-1 (-/-) null mice with TRAMP mice to generate TRAMP/Cav-1 (+/+) and TRAMP/Cav-1 (-/-) mice. Then, we assessed the expression of FASN in Cav-1 (+/+) and Cav-1 (-/-) prostate tumors by immunohistochemistry and Western blot analysis. Interestingly, our results indicate that FASN fails to be upregulated in Cav-1 (-/-) tumors. Importantly, the tumors examined were the same morphological grade, but Cav-1 (-/-) tumors were dramatically smaller and did not metastasize efficiently. We conclude that Cav-1 expression is normally required for the upregulation of FASN during prostate cancer progression. These results also mechanistically explain why TRAMP/Cav-1 (-/-) mice are dramatically resistant to the development of prostate tumors and lung metastases, as they lack the expression of the FASN tumor promoter. Thus, TRAMP/Cav-1 (-/-) mice will provide a novel model system to elucidate the role of FASN in prostate tumor progression. In addition, our results provide the first molecular genetic evidence that Cav-1 functions upstream of FASN during prostate cancer progression.

Trypanosoma cruzi infection induces proliferation of vascular smooth muscle cells.

ABSTRACT Trypanosoma cruzi infection causes cardiomyopathy and vasculopathy. Previous studies have demonstrated that infection of human umbilical vein endothelial and smooth muscle cells resulted in activation of extracellular signal-regulated kinase (ERK). In the present study, smooth muscle cells were infected with trypomastigotes, and immunoblot analysis revealed an increase in the expression of cyclin D1 and proliferating cell nuclear antigen (PCNA), important mediators of smooth muscle cell proliferation. Interestingly, after infection, the expression of caveolin-1 was reduced in both human umbilical vein endothelial cells and smooth muscle cells. Immunoblot and immunohistochemical analyses of lysates of carotid arteries obtained from infected mice revealed increased expression of PCNA, cyclin D1, its substrate, phospho-Rb (Ser780), and phospho-ERK1/2. The expression of the cyclin-dependent kinase inhibitor p21Cip1/Waf1, caveolin-1, and caveolin-3 was reduced in carotid arteries obtained from infected mice. There was an increase in the abundance of pre-pro-endothelin-1 mRNA in the carotid artery and aorta from infected mice. The ETA receptor was also elevated in infected arteries. ERK activates endothelin-1, which in turn exerts positive feedback activating ERK, and cyclin D1 is a downstream target of both endothelin-1 and ERK. There was significant incorporation of bromodeoxyuridine into smooth muscle cell DNA when treatment was with conditioned medium obtained from infected endothelial cells. Taken together, these data suggest that T. cruzi infection stimulates smooth muscle cell proliferation and is likely a result of the upregulation of the ERK-cyclin D1-endothelin-1 pathway.

Chapter 10 Caveolae and Caveolins in the Vascular System: Functional Roles in Endothelia, Macrophages, and Smooth Muscle Cells

Publisher Summary This chapter focuses on the two main cell types in the vasculature: endothelia and smooth muscle cells. These cell types are implicated in most homeostatic, as well as pathological, conditions of the vascular system. The chapter also focuses on the importance of macrophages in this system. The vascular system transports blood through the body in hollow tubular structures called blood vessels. The blood vessel is a dynamic structure that provides necessary “irrigation” to all the organs and tissues. The vessel wall is composed of three inter-connected layers: the intima, the media, and the adventitia. The intima contains a monolayer of endothelial cells (ECs) that is attached to a basement membrane formed by extracellular matrix proteins. In contrast, the medial layer is composed mainly of smooth muscle cells surrounded by extracellular matrix. The adventitial layer consists of fibroblasts, collagen, and elastic fibers, and is irrigated by the vasa vasora in the case of larger vessels.

Caveolin-1 Promotes Tumor Progression in an Autochthonous Mouse Model of Prostate Cancer: Genetic Ablation of Cav-1 Delays Advanced Prostate Tumor Development in Tramp Mice

Caveolin-1 (Cav-1) is the primary structural component of caveolae and is implicated in the processes of vesicular transport, cholesterol balance, transformation, and tumorigenesis. Despite an abundance of data suggesting that Cav-1 has transformation suppressor properties both in vitro and in vivo, Cav-1 is expressed at increased levels in human prostate cancer. To investigate the role of Cav-1 in prostate cancer onset and progression, we interbred Cav-1(-/-) null mice with a TRAMP (transgenic adenocarcinoma of mouse prostate) model that spontaneously develops advanced prostate cancer and metastatic disease. We found that, although the loss of Cav-1 did not affect the appearance of minimally invasive prostate cancer, its absence significantly impeded progression to highly invasive and metastatic disease. Inactivation of one (+/-) or both (-/-) alleles of Cav-1 resulted in significant reductions in prostate tumor burden, as well as decreases in regional lymph node metastases. Moreover, further examination revealed decreased metastasis to distant organs, such as the lungs, in TRAMP/Cav-1(-/-) mice. Utilizing prostate carcinoma cell lines (C1, C2, and C3) derived from TRAMP tumors, we also showed a positive correlation between Cav-1 expression and the ability of these cells to form tumors in vivo. Furthermore, down-regulation of Cav-1 expression in these cells, using a small interfering RNA approach, significantly reduced their tumorigenic and metastatic potential. Mechanistically, we showed that loss or down-regulation of Cav-1 expression results in increased apoptosis, with increased prostate apoptosis response factor-4 and PTEN levels in Cav-1(-/-) null prostate tumors. Our current findings provide the first in vivo molecular genetic evidence that Cav-1 does indeed function as a tumor promoter during prostate carcinogenesis, rather than as a tumor suppressor.