Oncogenic H-Ras V12 promotes anchorage-independent cytokinesis in human fibroblasts

Abstract

Cell anchorage is required for cell proliferation of untransformed cells, whereas anchorage-independent growth can be induced by oncogenes and is a hallmark of transformation. Whereas anchorage-dependent control of the progression of the G1 phase of the cell cycle has been extensively studied, it is less clear whether and how anchorage may control other cell cycle phases and whether oncogenes may affect such controls. Here, we found that lack of cell anchorage did not influence progression through the cell cycle S phase, G2 phase, or most of mitosis of primary human fibroblasts. However, unanchored fibroblasts could not complete cytokinesis. The cleavage furrow and central spindle were still formed in the absence of anchorage, but cells were unable to complete ingression, causing binucleation. Importantly, V12 H-Ras-transformed fibroblasts and two cancer cell lines progressed through the entire cell cycle without anchorage, including through cytokinesis. This indicates that oncogenic signaling may contribute to anchorageindependent growth and tumorigenesis by promoting the final cleavage furrow ingression during cytokinesis.cell adhesion ͉ integrin ͉ extracellular matrix ͉ signaling ͉ cell cycle

The metastatic cancer cell cortex: An adaptation to enhance robust cell division in novel environments?

“…One might imagine, therefore, that when placed in a non-adhesive environment, cells might face difficulties in division. This is indeed the case for human fibroblasts, which when entering mitosis in suspension, suffer a critical failure in cytokinesis, an effect that can be rescued by transformation with oncogenic Ras [11].…”

“…Moreover, circulating tumor cells have been reported to express proliferation markers [13]. Then, in order to form metastases, cells must undergo a process of extravasation to leave the blood/lymphatic system to colonize a new tissue environment, where they must proliferate despite differences in matrix composition and mechanics compared with their tissue of origin.microenvironment affect spindle positioning and division [7][8][9][10][11] it is likely that mitosis in a foreign environment presents a challenge. This may explain, in part, why metastasized cells often initially enter a dormant non-proliferative phase when introduced to a new environment [12].…”

Anchorage-independent cytokinesis as part of oncogenic transformation?

“…28 In contrary, we found that human primary fibroblasts progressed through mitosis until cytokinesis when cultured without anchorage, and that the tubulin spindles were still formed and sister chromatids separated in suspension. 25 Further, the central spindle was formed and contained tubulin, Aurora B and Rho A similar to the anchored cells , and also the midbody was formed in primary human fibroblasts cultured in suspension. 25 Importantly, lack of anchorage appears to play a role during cytokinesis, since several studies published almost 30 years ago described the formation of bi-nucleated cells caused by culture without proper substratum.…”

“…However, human primary fibroblasts progress perfectly through the S-and G 2 -phases without anchorage. 25 Nevertheless, it may be indicated from visual inspection that anchoring proteins and cytoskeleton remodeling might regulate some of the stages during mitosis. Onset of mitosis coincide with cellular de-adhesion and actin cytoskeleton remodeling inducing cell rounding that is prominent during prometaphaseanaphase (Fig.…”

“…1B). 25,26 Whether lack of anchorage influences early stages of mitosis is still controversial but it appears likely that too strong attachment might influence cell rounding and progression through prometaphase until telophase. Two recent studies focusing on the function of integrin β1 during mitosis suggest that it is important for progression through this period.…”