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Proliferation and migration of Smooth muscle cells (SMCs) are the key pathophysiological processes regulating vascular remodelling and atherosclerosis. Members of the epidermal growth factor receptor (EGFR) have been identified as a major participant of such processes. Although the direct involvement of EGFR is extensively studied, the indirect involvement such as via receptor cross-talk has not been carefully studied. Egr-1 is the zinc-finger transcription factor that serves as a master regulator of the inducible transcription of many genes implicated in the development of atherosclerosis and other chronic diseases. The complex signalling mechanism in the induction of this transcription factor is still poorly understood, despite its well-established signal processing (activation upon the binding of agonist to a receptor). The first study in this thesis explored the involvement of IL-1β in EGFR-induced Egr-1 expression in SMCs. We identified that HB-EGF does not require IL-1β signalling mechanism however, another ligand, EGF may require the IL-1β a signalling network to induce Egr-1 in SMC. The complicated signalling manner is still poorly understood. The second study investigated the mechanism behind the Egr-1 induction via IGF-1 and EGFR. In SMCs, it was discovered that MMPs/ADAMs and EGFR may play essential roles in signalling via IGF-1-EGFR-ERK1/2-Egr-1. These findings also provide possible mechanisms by which MMPs may be regulated by ADAMs, emphasising the role of MMPs/ADAMs and EGFR in IGF-1 induced Egr-1.The third study contributed to the degradation mechanism of Niemann-Pick C1 (NPC1). NPC1 is the essential protein that is involved in cholesterol trafficking hence dysfunction of this gene is fatal. PI3K-Akt-mTORC1 pathway was initially identified as a degradation pathway of NPC1 from our lab. In this study, the high level of phospho-Akt activation accelerated the degradation of NPC1 and the absence of the NPC1 in the cells affected both growth and proliferat

Null mutations of the Niemann-Pick type C1 (NPC1) gene cause NPC disease, a lysosomal storage disorder characterized by cholesterol accumulation in late endosomes (LE) and lysosomes (Ly).Nascent ormutated NPC1 is degraded through the ubiquitin-proteasome pathway, but how NPC1 degradation is regulated remains currently unknown. In the present study, we demonstrated a link between NPC1 degradation and the Akt (protein kinase B)/mTOR [mammalian (or mechanistic) target of rapamycin] signalling pathway in cervical cancer cell lines. We provided evidence that activated Akt/mTOR pathway increased NPC1 degradation by ∼50% in C33A cells when compared with SiHa or HeLa cells. NPC1 degradation in C33A cells was reversed when Akt/mTOR activation was blocked by specific inhibitors or when mTORC1 (mTOR complex 1) was disrupted by regulatory associated protein of mTOR (Raptor) knockdown. Importantly, inhibition of the Akt/mTOR pathway led to decreased NPC1 ubiquitination in C33A cells, pointing to a role of Akt/mTOR in the proteasomal degradation of NPC1. Moreover, we found that NPC1 depletion in several cancer cell lines inhibited cell proliferation and migration. Our results uncover Akt as a key regulator of NPC1 degradation and link NPC1 to cancer cell proliferation and migration.