The induction of endoreduplication and polyploidy by elevated expression of 14-3-3γ

Abstract

Several studies have demonstrated that specific 14-3-3 isoforms are frequently elevated in cancer and that these proteins play a role in human tumorigenesis. 14-3-3γ, an isoform recently demonstrated to function as an oncoprotein, is overexpressed in a variety of human cancers; however, its role in promoting tumorigenesis remains unclear. We previously reported that overexpression of 14-3-3γ caused the appearance of polyploid cells, a phenotype demonstrated to have profound tumor promoting properties. Here we examined the mechanism driving 14-3-3γ-induced polyploidization and the effect this has on genomic stability. Using FUCCI probes we showed that these polyploid cells appeared when diploid cells failed to enter mitosis and subsequently underwent endoreduplication. We then demonstrated that 14-3-3γ-induced polyploid cells experience significant chromosomal segregation errors during mitosis and observed that some of these cells stably propagate as tetraploids when isolated cells were expanded into stable cultures. These data lead us to conclude that overexpression of the 14-3-3γ promotes endoreduplication. We further investigated the role of 14-3-3γ in human NSCLC samples and found that its expression is significantly elevated in polyploid tumors. Collectively, these results suggests that 14-3-3γ may promote tumorigenesis through the production of a genetically unstable polyploid intermediate.

Measuring DNA content in live cells by fluorescence microscopy

“…4 c). Collectively, the expression of H2B-GFP combined with the quantification of DNA content—as outlined in this protocol—enables DNA ploidy to be correlated with several cellular parameters, and was recently employed to examine the length of mitosis and to enumerate the frequency of mitotic errors in polyploid cells induced by overexpression of YWHAG [ 11 ].

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“…Our method of measuring DNA content at the end of a time-lapse experiment was recently performed to study polyploid cells as they progressed through cell division [ 11 ]. We reasoned that polyploid cells could be identified using our method, as DNA content and DNA ploidy are interdependent.…”

“…We also demonstrate how this method, when used in combination with a histone 2B-GFP fusion protein, can be employed to monitor chromosomal dynamics in cells of varying ploidies (2n, 4n, 8n); an approach we recently used to examine the length of mitosis and the frequency of mitotic errors in polyploid cells induced by the overexpression of YWHAG [ 11 ]. To that end, cells with polyploid DNA content have recently been demonstrated to facilitate rapid adaptation in human tumors through significantly elevated rates of genomic aberrations, ranging from single nucleotide changes to whole chromosome gains and losses [ 12 ].…”

Cisplatin resistant ovarian cancer cells reveal a polyploid phenotype with remarkable activation of nuclear processes

“…A study by Sharma et al determined that the mTOR signaling pathway, a known regulator of cell metabolism, plays an important role in the polyploidy state in cancer cells. Moreover, Other studies have also shown the importance of HIPPO, 14-3-3 and Hypoxia signaling pathways in the induction of polyploidy in tumor cells [11][12][13][14][15].…”

The CD44high Subpopulation of Multifraction Irradiation-Surviving NSCLC Cells Exhibits Partial EMT-Program Activation and DNA Damage Response Depending on Their p53 Status

“…One of the potential sources of stem cells is polyploid cells characterized by multinucleation and cell cycle arrest [ 10 , 11 ]. Polyploidy was shown as an adaptation mechanism that allows cancers to tolerate harsh treatment conditions and plays significant role in the drug-resistance of many cancers and cancer cell lines, including NSCLC [ 12 , 13 ]. The polyploid giant cancer cells (PGCCs) could reversibly enter the therapy-induced senescence, allowing them to survive therapy and later re-enter the cell cycle to form daughter cells of typical size and ploidy [ 14 , 15 ].…”