The association of cyclin A and cyclin kinase inhibitor p21 in response to γ-irradiation requires the CDK2 binding region, but not the Cy motif

Hypoxia Changes Energy Metabolism and Growth Rate in Non-Small Cell Lung Cancer Cells

Hypoxia occurs in 80% of non-small cell lung carcinoma (NSCLC) cases, leading to treatment resistance. Hypoxia's effects on NSCLC energetics are not well-characterized. We evaluated changes in glucose uptake and lactate production in two NSCLC cell lines under hypoxia in conjunction with growth rate and cell cycle phase distribution. The cell lines A549 (p53 wt) and H358 (p53 null) were incubated under hypoxia (0.1% and 1% O₂) or normoxia (20% O₂). Glucose and lactate concentrations in supernatants were measured using luminescence assays. Growth kinetics were followed over seven days. Cell nuclei were stained with DAPI and nuclear DNA content was determined by flow cytometry to determine cell cycle phase. Gene expression under hypoxia was determined by RNA sequencing. Glucose uptake and lactate production under hypoxia were greater than under normoxia. They were also significantly greater in A549 compared to H358 cells. Faster energy metabolism in A549 cells was associated with a higher growth rate in comparison to H358 cells under both normoxia and hypoxia. In both cell lines, hypoxia significantly slowed down the growth rate compared to proliferation under normoxic conditions. Hypoxia led to redistribution of cells in the different cycle phases: cells in G1 increased and the G2 population decreased. Glucose uptake and lactate production increase under hypoxia in NSCLC cells indicated greater shunting of glucose into glycolysis rather than into oxidative phosphorylation compared to normoxia, making adenosine triphosphate (ATP) production less efficient. This may explain the redistribution of hypoxic cells in the G1 cell cycle phase and the time increase for cell doubling. Energy metabolism changes were more prominent in faster-growing A549 cells compared to slower-growing H358 cells, indicating possible roles for the p53 status and inherent growth rate of different cancer cells. In both cell lines, genes associated with cell motility, locomotion and migration were upregulated under chronic hypoxia, indicating a strong stimulus to escape hypoxic conditions.

The roles of nuclear myosin in the DNA damage response

Myosin within the nucleus has often been overlooked due to their importance in cytoplasmic processes and a lack of investigation. However, more recently, it has been shown that their nuclear roles are just as fundamental to cell function and survival with roles in transcription, DNA damage and viral replication. Myosins can act as molecular transporters and anchors that rely on their actin binding and ATPase capabilities. Their roles within the DNA damage response can varies from a transcriptional response, moving chromatin and stabilizing chromosome contacts. This review aims to highlight their key roles in the DNA damage response and how they impact nuclear organization and transcription.

Pelargonidin induces apoptosis and cell cycle arrest via a mitochondria mediated intrinsic apoptotic pathway in HT29 cells

Pelargonidin (PE) is an anticancer anthocyanidin that is abundant in berries.

Triptolide inhibits colon-rectal cancer cells proliferation by induction of G1 phase arrest through upregulation of p21

Triptolide, a diterpene triepoxide compound extracted from the traditional Chinese medicine herb Tripterygium wilfordii Hook F., is a potential cancer chemotherapeutic for tumors. However, the mechanism of anti-proliferative mechanism of triptolide in colon cancer cells is not entirely clear. Triptolide markedly inhibited HT29 and SW480 cells proliferation in a dose- and time-dependent manner. Triptolide decreased ERK and AKT phosphorylation, and GABPα expression in colon cancer cells. Beta-catenin expression and phosphorylation were not altered by incubation of triptolide. However, we found that triptolide repressed expression of LEF/TCF. Although it did not significantly affect cells apoptosis, triptolide induced G1 phase arrest dose-dependently. Further detection for the expression of cell cycle-related proteins suggesting that triptolide stimulate expression of p21 and repress cyclin A1. Increased p21 binded to CDK4/CDK6, therefore blocked function of CDK4/CDK6, and subsequently contribute to the G1 arrest. These data suggested that triptolide is a potential agent for treatment of colon cancer, and its anti-proliferation effect mainly occur through G1 phase arrest.

Only Akt1 is required for proliferation, while Akt2 promotes cell cycle exit through p21 binding

Protein kinase B (PKB/Akt) is an important modulator of insulin signaling, cell proliferation, and survival. Using small interfering RNA duplexes in nontransformed mammalian cells, we show that only Akt1 is essential for cell proliferation, while Akt2 promotes cell cycle exit. Silencing Akt1 resulted in decreased cyclin A levels and inhibition of S-phase entry, effects not seen with Akt2 knockdown and specifically rescued by microinjection of Akt1, not Akt2. In differentiating myoblasts, Akt2 knockout prevented myoblasts from exiting the cell cycle and showed sustained cyclin A expression. In contrast, overexpression of Akt2 reduced cyclin A and hindered cell cycle progression in M-G1 with increased nuclear p21. p21 is a major target in the differential effects of Akt isoforms, with endogenous Akt2 and not Akt1 binding p21 in the nucleus and increasing its level. Accordingly, Akt2 knockdown cells, and not Akt1 knockdown cells, showed reduced levels of p21. A specific Akt2/p21 interaction can be reproduced in vitro, and the Akt2 binding site on p21 is similar to that in cyclin A spanning T145 to T155, since (i) prior incubation with cyclin A prevents Akt2 binding, (ii) T145 phosphorylation on p21 by Akt1 prevents Akt2 binding, and (iii) binding Akt2 prevents phosphorylation of p21 by Akt1. These data show that specific interaction of the Akt2 isoform with p21 is key to its negative effect on normal cell cycle progression.

Identification of the region required for the antiapoptotic function of the cyclin kinase inhibitor, p21

The CDK inhibitor, p21, exhibits an antiapoptotic or proapoptotic effect, in addition to its anti-proliferative effect, depending on the conditions. To define the apoptosis-regulatory function of p21, we constructed cells that stably express C-terminal deletion mutants of p21 (full length 164aa), 1-157, 1-147 or 1-128, and evaluated the apoptotic response of these cells. The AnnexinV positive cell fraction after gamma-irradiation did not increase in cells expressing 1-157. Consistently, an increase of caspase3 activity or the active form of caspase3 was not observed in cells expressing 1-157, but was prominent in cells expressing 1-128 and 1-147. Further, the activity of caspase9 was suppressed in gamma-irradiated cells expressing 1-157. The antiapoptotic effect of 1-157 was weaker in Fas-induced apoptosis. Our data indicate that the 1-157 region of p21 inhibits apoptosis caused by gamma-irradiation by reducing the activity of caspase9 and caspase3, and the 148-157 region is critical for its inhibiting activity.