ABSTRACT
Loss of epithelial organization is a hallmark of carcinomas, but whether polarity regulates tumor growth and metastasis is poorly understood. To address this issue, we depleted the Par3 polarity gene by RNAi in combination with oncogenic Notch or Ras(61L) expression in the murine mammary gland. Par3 silencing dramatically reduced tumor latency in both models and produced invasive and metastatic tumors that retained epithelial marker expression. Par3 depletion was associated with induction of MMP9, destruction of the extracellular matrix, and invasion, all mediated by atypical PKC-dependant JAK/Stat3 activation. Importantly, Par3 expression is significantly reduced in human breast cancers, which correlates with active aPKC and Stat3. These data identify Par3 as a regulator of signaling pathways relevant to invasive breast cancer.
Subject(s)
Breast Neoplasms/metabolism , Cell Adhesion Molecules/genetics , Adaptor Proteins, Signal Transducing , Animals , Breast Neoplasms/pathology , Cell Adhesion Molecules/metabolism , Cell Adhesion Molecules/physiology , Cell Cycle Proteins/genetics , Cell Cycle Proteins/metabolism , Cell Polarity , Cell Proliferation , Cell Transformation, Neoplastic , Female , Gene Expression Regulation, Neoplastic , Humans , Mammary Neoplasms, Experimental/genetics , Mammary Neoplasms, Experimental/metabolism , Matrix Metalloproteinase 9/metabolism , Membrane Proteins/genetics , Membrane Proteins/metabolism , Mice , Neoplasm Metastasis , Phosphorylation , Protein Kinase C/metabolism , Proto-Oncogene Proteins p21(ras)/metabolism , Proto-Oncogene Proteins p21(ras)/physiology , RNA Interference , Tumor Cells, CulturedABSTRACT
The biosynthetic pathway carries cargos from the endoplasmic reticulum (ER) to the trans Golgi network (TGN) via a typical passage through the Golgi. Interestingly, large particles such as procollagen, chylomicrons and some viruses all reach the TGN by atypical routes. Given this dichotomy, we anticipated that such cargos might rely on non-classical machineries downstream of the TGN. Using Herpes simplex virus type 1 (HSV-1) as a model and a synchronized infection protocol that focuses on TGN to plasma membrane transport, the present study revealed the surprising implication of the cellular serine-threonine protein kinase D in HSV-1 egress. These findings, confirmed by a variety of complementary means [pharmacological inhibitors, dominant negative mutant, RNA interference and electron microscopy (EM)], identify one of possibly several cellular factors that modulate the egress of viruses transiting at the TGN. Moreover, the involvement of this kinase, previously known to regulate the transport of small basolateral cargos, highlights the trafficking of both small and exceptionally large entities by a common machinery downstream of the TGN, in sharp contrast to earlier steps of transport. Conceptually, this indicates the TGN is not only a sorting station from which cargos can depart towards different destinations but also a meeting point where conventional and unconventional routes can meet along the biosynthetic pathway. Lastly, given the apical release of HSV-1 in neurons, it opens up the possibility that this kinase might regulate some apical sorting.
