The protein synthetic surge in response to mitogen triggers high glycolytic enzyme levels in human lymphocytes and occurs prior to DNA synthesis

The Prognostic Value of PERK in Cancer and Its Relationship With Immune Cell Infiltration

Background: Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is a type I transmembrane protein that functions as an endoplasmic reticulum (ER) stress sensor to regulate global protein synthesis. Recent research studies suggest that PERK, as an important receptor protein of unfolded protein response, is involved in the pathogenesis of many cancers. This study aimed to investigate PERK expression and its relationship with prognosis in pan-cancer and attempted to explore the relevant mechanism of PERK involved in the regulation of cancer pathogenesis.

Methods: The Oncomine and TIMER databases were used to analyze the expression of PERK between pan-cancer samples and normal samples. Survival analysis was performed using the PrognoScan, Kaplan–Meier (K-M) plotter, and UALCAN databases. Gene set enrichment analysis (GSEA) was used to perform the functional enrichment analysis of the PERK gene in breast invasive carcinoma (BRCA), head and neck squamous cell carcinoma (HNSC), and thyroid carcinoma (THCA). The TIMER database was used to investigate the correlation between PERK expression and tumor-infiltrating immune cells and analyze the relationship of PERK with marker genes of immune cells which were downloaded from the CellMarker database in BRCA, HNSC, and THCA.

Results: PERK was differentially expressed in various cancers, such as breast cancer, liver cancer, lung cancer, gastric carcinoma, lymphoma, thyroid cancer, leukemia, and head and neck squamous cell carcinomas. The high expression of PERK was associated with a poor prognosis in KIRP, LGG, BRCA, and THCA and with a favorable prognosis in HNSC. The results of GSEA indicated that PERK was mainly enriched in immune-related signaling pathways in BRCA, HNSC, and THCA. Moreover, PERK expression was significant positively correlated with infiltrating levels of macrophages and dendritic cells and was strongly associated with a variety of immune markers, especially macrophage mannose receptor 1 (MRC1, also called CD206) and T-helper cells (Th).

Conclusion: The high expression of PERK could promote the infiltration of multiple immune cells in the tumor microenvironment and could deteriorate the outcomes of patients with breast and thyroid cancers, suggesting that PERK as well as tumor-infiltrating immune cells could be taken as potential biomarkers of prognosis.

Sigma Receptors as Endoplasmic Reticulum Stress "Gatekeepers" and their Modulators as Emerging New Weapons in the Fight Against Cancer

Despite the interest aroused by sigma receptors (SRs) in the area of oncology, their role in tumor biology remains enigmatic. The predominant subcellular localization and main site of activity of SRs are the endoplasmic reticulum (ER). Current literature data, including recent findings on the sigma 2 receptor subtype (S2R) identity, suggest that SRs may play a role as ER stress gatekeepers. Although SR endogenous ligands are still unknown, a wide series of structurally unrelated compounds able to bind SRs have been identified. Currently, the identification of novel antiproliferative molecules acting via SR interaction is a challenging task for both academia and industry, as shown by the fact that novel anticancer drugs targeting SRs are in the preclinical-stage pipeline of pharmaceutical companies (i.e., Anavex Corp. and Accuronix). So far, no clinically available anticancer drugs targeting SRs are still available. The present review focuses literature advancements and provides a state-of-the-art overview of SRs, with emphasis on their involvement in cancer biology and on the role of SR modulators as anticancer agents. Findings from preclinical studies on novel anticancer drugs targeting SRs are presented in brief.

Endoplasmic reticulum proteostasis: a key checkpoint in cancer

The unfolded protein response (UPR) is an intracellular signaling network largely controlled by three endoplasmic reticulum (ER) transmembrane proteins, inositol-requiring enzyme 1α, PRK-like ER kinase, and activating transcription factor 6, that monitor the protein-folding status of the ER and initiate corrective measures to maintain ER homeostasis. Hypoxia, nutrient deprivation, proteasome dysfunction, sustained demands on the secretory pathway or somatic mutations in its client proteins, conditions often encountered by cancer cells, can lead to the accumulation of misfolded proteins in the ER and cause "ER stress." Under remediable levels of ER stress, the homeostatic UPR outputs activate transcriptional and translational changes that promote cellular adaptation. However, if the ER stress is irreversible despite these measures, a terminal UPR program supersedes that actively signals cell destruction. In addition to its prosurvival and prodeath outputs, the UPR is now recognized to play a major role in the differentiation and activation of specific immune cells, as well as proinflammatory cytokine production in many cell types. Given the numerous intrinsic and extrinsic factors that threaten the fidelity of the secretory pathway in cancer cells, it is not surprising that ER stress is documented in many solid and hematopoietic malignancies, but whether ongoing UPR signaling is beneficial or detrimental to tumor growth remains hotly debated. Here I review recent evidence that cancer cells are prone to loss of proteostasis within the ER, and hence may be susceptible to targeted interventions that either reduce homeostatic UPR outputs or alternatively trigger the terminal UPR.

c-Myc activates multiple metabolic networks to generate substrates for cell-cycle entry

Cell proliferation requires the coordinated activity of cytosolic and mitochondrial metabolic pathways to provide ATP and building blocks for DNA, RNA and protein synthesis. Many metabolic pathway genes are targets of the c-myc oncogene and cell-cycle regulator. However, the contribution of c-Myc to the activation of cytosolic and mitochondrial metabolic networks during cell-cycle entry is unknown. Here, we report the metabolic fates of [U-(13)C] glucose in serum-stimulated myc(-/-) and myc(+/+) fibroblasts by (13)C isotopomer NMR analysis. We demonstrate that endogenous c-myc increased (13)C labeling of ribose sugars, purines and amino acids, indicating partitioning of glucose carbons into C1/folate and pentose phosphate pathways, and increased tricarboxylic acid cycle turnover at the expense of anaplerotic flux. Myc expression also increased global O-linked N-acetylglucosamine protein modification, and inhibition of hexosamine biosynthesis selectively reduced growth of Myc-expressing cells, suggesting its importance in Myc-induced proliferation. These data reveal a central organizing function for the Myc oncogene in the metabolism of cycling cells. The pervasive deregulation of this oncogene in human cancers may be explained by its function in directing metabolic networks required for cell proliferation.

Cytogenetic study of the induction mechanism of chromosome-type aberrations by 1-beta-D-arabinofuranosylcytosine

Treatment of human lymphocytes in the G(1) phase with 1-beta-D-arabinofuranosylcytosine (AraC) results in the formation of chromosome-type aberrations, e.g., dicentric or ring chromosomes. Generally, it is accepted that DNA double-strand breaks (DSBs) cause chromosome-type aberrations. However, AraC lacks the functional groups necessary to induce such breaks, suggesting that it does not induce DSBs directly. In this study, we show that induction of DSBs is not mediated by direct action by AraC on DNA. Second, we demonstrate that the induction of DSBs or chromosome-type aberrations by AraC in human lymphocytes is inhibited by cycloheximide (CHM), an inhibitor of protein synthesis. These data suggest that newly synthesized proteins in AraC-treated lymphocytes mediate the induction of the DSBs. Thus, we suggest that AraC-induced endonucleolytic protein(s) in lymphocytes mediate the formation of chromosome-type aberrations.

Inhibition of the G1-S transition of the cell cycle by inhibitors of deoxyhypusine hydroxylation

The formation of the unusual amino-acid hypusine in eIF-5A (eukaryotic initiation factor 5A) is associated with cellular proliferation. We used a panel of compounds, including mimosine, to probe the relationship between the exit from the G1 phase of the cell cycle, i.e., the onset of DNA replication, and the formation of hypusine by the enzyme deoxyhypusyl hydroxylase (DOHH). These two parameters displayed the same dose dependency and structure-activity relationship. Only compounds that inhibited DOHH also suppressed proliferation. This effect was observed: (i) in spontaneously proliferating, virally transformed, and mitogen-stimulated cells; (ii) for both anchorage-dependent and anchorage-independent proliferation; and (iii) with normal and malignant cell lines. DOHH reactivation occurred rapidly after inhibitor withdrawal and correlated with synchronized entry into S. The changes in the expression of specific genes during the G1-to-S transition mimicked the physiological pattern. These findings suggest that hypusine formation in eIF-5A which occurs in a specific, invariant sequence motif acquired early in evolution, may be involved in the G1-to-S transition in the eukaryotic cells tested.

Metabolic changes in activated T cells: an NMR study of human peripheral blood lymphocytes

Using NMR spectroscopy, we studied purified, human T lymphocytes in a serum-free medium. Purified cells were entrapped inside agarose beads and induced to proliferate by the mitogens phorbol-12-myristate-13-acetate and ionomycin. T lymphocytes in standard culture and inside agarose beads exhibit comparable viability, and similar extent and kinetics of DNA synthesis and interleukin-2 secretion. 31P-NMR revealed decreased phosphomonoester and increased phosphodiester content in cells stimulated for two days or longer. 13C-glucose utilization and 13C-lactate production rates showed that 85% of the utilized glucose was converted to lactate. 1H-NMR spectra of the perfusing media indicated that lactate was also produced from substrates other than glucose or glycogen. Glucose accounted for 25% of the lactate produced by quiescent cells, and for 67% of lactate production by stimulated cells. Glycolysis was enhanced 6-fold within the first 2 hours following stimulation, and 15-fold by 48 or 96 h. Aerobic lactate production was increased 3-fold by 48 h, with only a minor enhancement during the first 12 h of stimulation. Our results indicate a shift from mostly aerobic to mostly anaerobic lactate production in T lymphocytes within the first 90 min of the G0 to G1 transition during cell cycle progression.