Biology subjects

Akman, H. B.

Publications and source records attributed to Akman, H. B..

4 recordsLinked to original sources

bioRxiv2024

CXXC5 is a ubiquitinated protein and is degraded by the ubiquitination-proteasome pathway

CXXC5 as a member of the zinc-finger CXXC family proteins interacts with unmodified CpG dinucleotides to modulate the expression of genes involved in cellular proliferation, differentiation, and death in physiology and pathophysiology. Various signaling pathways including mitogenic estrogens, particularly 17{beta}-estradiol (E2), contribute to the expression and synthesis of CXXC5. However, how signaling pathways modulate protein levels of CXXC5 in cells is largely unknown. We previously reported that some key regulators, including retinoblastoma 1 and E74 Like ETS Transcription Factor 1, of the G1 to S phase transitions are involved in the expression of CXXC5 in estrogen-responsive MCF7 cells, derived from a breast adenocarcinoma. We, therefore, predict that the synthesis of CXXC5 is regulated in a cell cycle-dependent manner. We report here that although E2 in synchronized MCF7 cells augments both transcription and synthesis of CXXC5 in the G1 phase, CXXC5 protein levels are primarily mediated by ubiquitination independently of cell cycle phases. Utilizing the bioUbiquitination approach, which is based on cellular biotinylation of ubiquitin, in HEK293FT cells derived from immortalized human embryonic kidney cells followed by sequential immunoprecipitation coupled mass spectrometry analyses, we identified multiple ubiquitinated lysine residues of CXXC5. We show in both MCF7 and HEK293FT cells that the ubiquitinated lysine residues contribute to the degradation of CXXC5 through the ubiquitin-proteasome pathway.

cell biology↗

bioRxiv2023

Differential translation of mRNA isoforms underlies oncogenic activation of cell cycle kinase Aurora A

Aurora Kinase A (AURKA) is an oncogenic kinase with major roles in mitosis, but also exerts cell cycle- and kinase-independent functions linked to cancer. Therefore control of its expression, as well as its activity, is crucial. A short and a long 3UTR isoform exist for AURKA mRNA, resulting from alternative polyadenylation (APA). We initially observed that in Triple Negative Breast Cancer, where AURKA is typically overexpressed, the short isoform is predominant and this correlates with faster relapse times of patients. The short isoform is characterized by higher translational efficiency since translation and decay rate of the long isoform are targeted by hsa-let-7a tumor-suppressor miRNA. Additionally, hsa-let-7a regulates the cell cycle periodicity of translation of the long isoform, whereas the short isoform is translated highly and constantly throughout interphase. Finally, disrupted production of the long isoform led to an increase in proliferation and migration rates of cells. In sum, we uncovered a new mechanism dependent on the cooperation between APA and miRNA targeting likely to be a route of oncogenic activation of human AURKA.

cell biology↗

bioRxiv2022

Revisiting degron motifs in human AURKA required for its targeting by APC/C-FZR1

Mitotic kinase Aurora A (AURKA) diverges from other kinases in its multiple active conformations that may explain its interphase roles and association with cancer, and the limited efficacy of drugs targeting the kinase pocket. Regulation of AURKA activity by the cell is critically dependent on destruction mediated by the Anaphase-Promoting Complex (APC/CFZR1) during mitotic exit and G1 phase and requires an atypical N-terminal degron in AURKA called the A-box in addition to a reported canonical D-box degron in the C-terminus. Here we find that the proposed C-terminal D-box of AURKA does not act as a degron and instead mediates essential structural features of the protein. In living cells, as previously reported in vitro, the N-terminal intrinsically disordered region (IDR) of AURKA containing the A-box is sufficient to confer FZR1-dependent mitotic degradation. Both in silico and in cellulo assays predict the QRVL Short Linear Interacting Motif (SLiM) of the A-box to be a phospho-regulated D-box. We propose that degradation of full-length AURKA additionally depends on an intact C-terminal domain because of critical conformational parameters permissive for both activity and mitotic degradation of AURKA. Summary blurbAURKA degron motifs are redefined to show that the so-called N-terminal A-box is in fact a D-box, and the so-called D-box in the C-terminus is not a degron but a motif critical for the active, degradable conformation of AURKA

cell biology↗

bioRxiv2019

AURKA destruction is decoupled from its activity at mitotic exit but suppresses interphase activity

Activity of AURKA is controlled through multiple mechanisms including phosphorylation, ubiquitin-mediated degradation, and allosteric interaction with TPX2. Activity peaks at mitosis before AURKA is degraded during mitotic exit in a process strictly dependent on APC/C coactivator FZR1. We used FZR1 knockout cells (FZR1KO) and a novel FRET-based AURKA biosensor to investigate how activity is regulated in absence of destruction. We found that AURKA activity in FZR1KO cells dropped at mitotic exit as rapidly as in parental cells, despite absence of destruction. Unexpectedly, TPX2 was degraded normally in FZR1KO cells. Overexpression of an N-terminal TPX2 fragment sufficient for AURKA binding, but not degraded at mitotic exit, caused delay in AURKA inactivation. We conclude that AURKA inactivation in mitotic exit is determined not by its own degradation but by degradation of TPX2 and therefore dependent on CDC20 rather than FZR1. The biosensor revealed that FZR1 instead suppresses AURKA activity in interphase and is critically required for assembly of the interphase mitochondrial network after mitosis.

cell biology↗