Molecular genetic analysis of VRK1 in mammary epithelial cells: depletion slows proliferation in vitro and tumor growth and metastasis in vivo

Abstract

The vaccinia-related kinases (VRKs) comprise a branch of the casein kinase family. VRK1, a ser/thr kinase with a nuclear localization, is the most well-studied paralog and has been described as a proproliferative protein. In lower eukaryotes, a loss of VRK1 activity is associated with severe mitotic and meiotic defects. Mice that are hypomorphic for VRK1 expression are infertile, and depletion of VRK1 in tissue culture cells can impair cell proliferation and alter several signaling pathways. VRK1 has been implicated as part of a ‘gene-expression signature' whose overexpression correlates with poor clinical outcome in breast cancer patients. We present here our investigation of the role of VRK1 in the growth of normal (MCF10) and malignant (MDA-MB-231) human mammary epithelial cells, and demonstrate that shRNA-mediated depletion of VRK1 slows their proliferation significantly. Conversely, stable overexpression of a FLAG-tagged VRK1 transgene imparts a survival advantage to highly malignant MDA-MB-231 cells under conditions of nutrient and growth factor deprivation. Moreover, in a murine orthotopic xenograft model of breast cancer, we demonstrate that tumors depleted of VRK1 show a 50% reduction in size from 4–13 weeks postengraftment. The incidence and burden of distal metastases in the lungs and brain was also significantly reduced in mice engrafted with VRK1-depleted cells. These studies demonstrate that VRK1 depletion or overexpression has an impact on the proliferation and survival of cell lines derived from normal or malignant mammary tissue, and moreover show that depletion of VRK1 in MDA-MB-231 cells reduces their oncogenic and metastatic properties in vivo.

EWS-FLI1 Utilizes Divergent Chromatin Remodeling Mechanisms to Directly Activate or Repress Enhancer Elements in Ewing Sarcoma

“…S5E and F ). In contrast, VRK1 depletion in non-Ewing sarcoma cell lines only moderately decreased proliferation and failed to trigger apoptosis, consistent with recent studies of its function in other tumor models (Kim et al, 2013; Molitor and Traktman, 2013). Finally, injection of VRK1-depleted SKNMC cells immediately after lentiviral infection resulted in a marked decrease in tumor development in vivo (p-value < 10 −5 ), confirming the critical role of this direct target in sustaining tumor cell proliferation and survival (Fig.…”

Overexpression of the VRK1 kinase, which is associated with breast cancer, induces a mesenchymal to epithelial transition in mammary epithelial cells

“…VRK1 overexpression does not affect cellular doubling time [this paper and [5]] or lead to the changes in cell morphology or monolayer appearance that are associated with transformation. The work described herein provides a new perspective by revealing that VRK1 overexpression augments the epithelial properties of cells in culture.…”

Oncogenic Sox2 regulates and cooperates with VRK1 in cell cycle progression and differentiation

“…VRK1 is strong facilitator of cell cycle progression1517 and proliferation1730, and many tumors have very high levels of VRK1 protein which is consistent with an oncogenic function of wild-type VRK1. High levels of VRK15253 and Sox25455 are markers of a poorer prognosis in breast cancer, which is a reflection of their contribution to expanding the tumor cell population.…”