Cyclin A Turns on Bora to Light the Path to Mitosis

CDC6 as a Key Inhibitory Regulator of CDK1 Activation Dynamics and the Timing of Mitotic Entry and Progression

Timely mitosis is critically important for early embryo development. It is regulated by the activity of the conserved protein kinase CDK1. The dynamics of CDK1 activation must be precisely controlled to assure physiologic and timely entry into mitosis. Recently, a known S-phase regulator CDC6 emerged as a key player in mitotic CDK1 activation cascade in early embryonic divisions, operating together with Xic1 as a CDK1 inhibitor upstream of the Aurora A and PLK1, both CDK1 activators. Herein, we review the molecular mechanisms that underlie the control of mitotic timing, with special emphasis on how CDC6/Xic1 function impacts CDK1 regulatory network in the Xenopus system. We focus on the presence of two independent mechanisms inhibiting the dynamics of CDK1 activation, namely Wee1/Myt1- and CDC6/Xic1-dependent, and how they cooperate with CDK1-activating mechanisms. As a result, we propose a comprehensive model integrating CDC6/Xic1-dependent inhibition into the CDK1-activation cascade. The physiological dynamics of CDK1 activation appear to be controlled by the system of multiple inhibitors and activators, and their integrated modulation ensures concomitantly both the robustness and certain flexibility of the control of this process. Identification of multiple activators and inhibitors of CDK1 upon M-phase entry allows for a better understanding of why cells divide at a specific time and how the pathways involved in the timely regulation of cell division are all integrated to precisely tune the control of mitotic events.

Adipose-Derived Stem Cells Inhibited the Proliferation of Bladder Tumor Cells by S Phase Arrest and Wnt/β-Catenin Pathway

Adipose-derived stem cells (ADSCs), which are present in most organs and tissues, were evaluated as a novel medium for stem cell therapy. In this study, we investigated the effects and underlying mechanisms of ADSCs in bladder tumor (BT) cells. SV-HUC, T24, and EJ cells were cultured with ADSCs and conditioned medium from ADSCs (ADSC-CM). We observed that in routine culture, ADSCs significantly inhibited the proliferation of T24 and EJ cells in a dose-dependent manner. In addition, ADSC-CM attenuated the viability of T24 and EJ cells in a dose-dependent manner. Cell cycle analysis indicated that ADSC-CM was capable of inducing T24 and EJ cells S phase arrest and downregulating the expression of CDK 1, whereas the expression of cyclin A was increased. ADSC-CM could induce apoptosis in T24 cells. The mechanism of this effect likely involved the caspase3/7 pathway and Wnt/β-catenin pathway. These findings demonstrated that ADSCs could inhibit the proliferation of BT cells via secretory factors.

Ferumoxytol and CpG oligodeoxynucleotide 2395 synergistically enhance antitumor activity of macrophages against NSCLC with EGFRL858R/T790M mutation

Purpose: Drug resistance is a major challenge for epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) treatment of lung cancer. Ferumoxytol (FMT) drives macrophage (MΦ) transformation towards a M1-like phenotype and thereby inhibits tumor growth. CpG oligodeoxynucleotide 2395 (CpG), a toll-like receptor 9 (TLR9) agonist, is an effective therapeutic agent to induce anticancer immune responses. Herein, the effect of co-administered FMT and CpG on MΦ activation for treating non-small cell lung cancer (NSCLC) was explored.

Methods: The mRNA expression levels of M1-like genes in RAW 264.7 MΦ cells stimulated by FMT, CpG and FMT and CpG (FMT/CpG) were evaluated by quantitative reverse transcription PCR (qRT-PCR). Then, the effects of FMT/CpG-pretreated MΦ supernatant on apoptosis and proliferation of H1975 cells were detected by flow cytometry, and the expression of EGFR and its downstream signaling pathway in H1975 cells were explored by western blotting. Finally, a H1975 cell xenograft mouse model was used to study the anti-tumor effect of the combination of FMT and CpG in vivo.

Results: FMT and CpG synergistically enhanced M1-like gene expression in MΦ, including tumor necrosis factor-α, interleukin (IL)-12, IL-1α, IL-1β, IL-6 and inducible nitric oxide synthase (iNOS). FMT/CpG-pretreated MΦ supernatant inhibited proliferation and induced apoptosis of H1975 cells, accompanied by down-regulation of cell cycle-associated proteins and up-regulation of apoptosis-related proteins. Further studies indicated that the FMT/CpG-pretreated MΦ supernatant suppressed p-EGFR and its downstream AKT/mammalian target of rapamycin signaling pathway in H1975 cells. Furthermore, FMT/CpG suppressed tumor growth in mice accompanied by a decline in the EGFR-positive tumor cell fraction and increased M1 phenotype macrophage infiltration.

Conclusion: FMT acted synergistically with CpG to activate MΦ for suppressed proliferation and promoted apoptosis of NSCLC cells via EGFR signaling. Thus, combining FMT and CpG is an effective strategy for the treatment of NSCLC with EGFR^L858R/T790M mutation.