The HECT E3 ubiquitin ligase NEDD4 interacts with and ubiquitylates SQSTM1 for inclusion body autophagy.

Our previous studies have shown that the HECT E3 ubiquitin ligase NEDD4 interacts with LC3 and is required for starvation and rapamycin-induced activation of autophagy. Here, we report that NEDD4 directly binds to SQSTM1 via its HECT domain and polyubiquitylates SQSTM1. This ubiquitylation is through K63 conjugation and is not involved in proteasomal degradation.

The E3 ubiquitin ligase NEDD4 is an LC3-interactive protein and regulates autophagy.

The MAP1LC3/LC3 family plays an essential role in autophagosomal biogenesis and transport. In this report, we show that the HECT family E3 ubiquitin ligase NEDD4 interacts with LC3 and is involved in autophagosomal biogenesis. NEDD4 binds to LC3 through a conserved WXXL LC3-binding motif in a region between the C2 and the WW2 domains.

PBK/TOPK mediates geranylgeranylation signaling for breast cancer cell proliferation.

PDZ binding-kinase (PBK) (also named T-lymphokine-activated killer cell-originated protein kinase (TOPK)), a serine/threonine kinase, is tightly controlled in normal tissues but elevated in many tumors, and functions in tumorigenesis and metastasis. However, the signaling that regulates expression of PBK in cancer cells remains elusive. Here we show that atorvastatin (Lipitor), an inhibitor of hydroxymethylglutaryl co-enzyme A (HMG-CoA) reductase that is a rate-limiting enzyme of mevalonate pathway, down-regulates expression of PBK by impairing protein geranylgeranylation.

COX-2 inhibitors arrest prostate cancer cell cycle progression by down-regulation of kinetochore/centromere proteins.

Background: Previous studies have shown that COX-2 inhibitors inhibit cancer cell proliferation. However, the molecular mechanism remains elusive.

Methods: Prostate cancer LNCaP, 22Rv1, and PC3 cells were cultured and treated with the COX-2 inhibitors celecoxib and CAY10404.

The activation mechanism of ACK1 (activated Cdc42-associated tyrosine kinase 1).

ACK [activated Cdc42 (cell division cycle 42)-associated tyrosine kinase; also called TNK2 (tyrosine kinase, non-receptor, 2)] is activated in response to multiple cellular signals, including cell adhesion, growth factor receptors and heterotrimeric G-protein-coupled receptor signalling. However, the molecular mechanism underlying activation of ACK remains largely unclear. In the present study, we demonstrated that interaction of the SH3 (Src homology 3) domain with the EBD [EGFR (epidermal growth factor receptor)-binding domain] in ACK1 forms an auto-inhibition of the kinase activity.

Atorvastatin induces autophagy in prostate cancer PC3 cells through activation of LC3 transcription.

Our previous studies have demonstrated that atorvastatin induces autophagy in the androgen receptor negative prostate cancer PC3 cells through inhibition of geranylgeranyl biosynthesis [Parikh et al., Prostate. 70(9): 971-981 (2010)].

Calcium activates Nedd4 E3 ubiquitin ligases by releasing the C2 domain-mediated auto-inhibition.

Nedd4 E3 ligases are members of the HECT E3 ubiquitin ligase family and regulate ubiquitination-mediated protein degradation. In this report, we demonstrate that calcium releases the C2 domain-mediated auto-inhibition in both Nedd4-1 and Nedd4-2. Calcium disrupts binding of the C2 domain to the HECT domain.

Statin-induced autophagy by inhibition of geranylgeranyl biosynthesis in prostate cancer PC3 cells.

Background: Autophagy is a cellular process of degradation of macromolecules and organelles and activated under nutritional stress. Statins are a class of inhibitors of 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a key enzyme in synthesis of cholesterol. Epidemiological studies have shown that statin use decreases the incidence of advanced prostate cancer.

HECT E3 ubiquitin ligase Nedd4-1 ubiquitinates ACK and regulates epidermal growth factor (EGF)-induced degradation of EGF receptor and ACK.

ACK (activated Cdc42-associated tyrosine kinase) (also Tnk2) is an ubiquitin-binding protein and plays an important role in ligand-induced and ubiquitination-mediated degradation of epidermal growth factor receptor (EGFR). Here we report that ACK is ubiquitinated by HECT E3 ubiquitin ligase Nedd4-1 and degraded along with EGFR in response to EGF stimulation. ACK interacts with Nedd4-1 through a conserved PPXY WW-binding motif.

Identification of the domain in ErbB2 that restricts ligand-induced degradation.

Ligand-induced receptor degradation is an important process for down-regulation of plasma membrane receptors. While epidermal growth factor receptor (EGFR) is rapidly internalised and degraded upon ligand stimulation, ErbB2, the closest member to EGFR in ErbB receptor family, is resistant in ligand-induced degradation. To understand the molecular mechanisms underlying the impairment in ligand-induced degradation of ErbB2, we attempted to determine structural factor in ErbB2 that restricts the degradation.

Activated Cdc42-associated kinase 1 is a component of EGF receptor signaling complex and regulates EGF receptor degradation.

Cdc42-associated tyrosine kinase 1 (ACK1) is a specific down-stream effector of Cdc42, a Rho family small G-protein. Previous studies have shown that ACK1 interacts with clathrin heavy chain and is involved in clathrin-coated vesicle endocytosis. Here we report that ACK1 interacted with epidermal growth factor receptor (EGFR) upon EGF stimulation via a region at carboxy terminus that is highly homologous to Gene-33/Mig-6/RALT.

Dimerization is required for SH3PX1 tyrosine phosphorylation in response to epidermal growth factor signalling and interaction with ACK2.

SH3PX1 [SNX9 (sorting nexin 9)] is a member of SNX super-family that is recognized by sharing a PX (phox homology) domain. We have previously shown that SH3PX1, phosphorylated by ACK2 (activated Cdc42-associated tyrosine kinase 2), regulates the degradation of EGF (epidermal growth factor) receptor. In mapping the tyrosine phosphorylation region, we found that the C-terminus of SH3PX1 is required for its tyrosine phosphorylation.

Interaction of activated Cdc42-associated tyrosine kinase ACK2 with HSP90.

ACK2 (activated Cdc42-associated tyrosine kinase 2) is a specific downstream effector for Cdc42, a member of the Rho family of small G-proteins. ACK2 interacts with clathrin, an endocytic vesicle coating protein, and SH3PX1, a sorting nexin, and is involved in clathrin-mediated endocytosis. While searching for proteins that interact with ACK2, we found that HSP90 (heat-shock protein 90) binds to ACK2.

Identification of the region in Cdc42 that confers the binding specificity to activated Cdc42-associated kinase.

The Rho family small G-protein Cdc42 has been implicated in a diversity of biological functions. Multiple downstream effectors have been identified. How Cdc42 discriminates the interaction with its multiple downstream effectors is not known.