Dichotomous role of protein kinase A type I (PKAI) in the tumor microenvironment: a potential target for 'two-in-one' cancer chemoimmunotherapeutics

Revisiting the roles of cAMP signalling in the progression of prostate cancer

Prostate cancer is one of the most common cancers in men and one of the top causes of death in men worldwide. Development and function of both normal prostate cells and early-stage prostate cancer cells are dependent on the cross-talk between androgen signalling systems and a variety of other transduction pathways which drive differentiation of these cells towards castration-resistance. One such signalling pathway is the ubiquitous cAMP signalling axis which functions to activate spatially restricted pools of cAMP effectors such as protein kinase A (PKA). The importance of both PKA and cAMP in the development of prostate cancer, and their interactions with the androgen receptor, were the focus of a review by Merkle and Hoffmann in 2010. In this updated review, we revisit this topic with analysis of current PKA-related prostate cancer literature and introduce novel information on the relevance of another cAMP effector, the exchange protein directly activated by cAMP (EPAC).

Association Between FSIP2 Mutation and an Improved Efficacy of Immune Checkpoint Inhibitors in Patients With Skin Cutaneous Melanoma

Background

Immune checkpoint inhibitors (ICIs) have shown remarkable success in treating skin cutaneous melanoma (SKCM); however, the response to treatment varies greatly between patients. Considering that the efficacy of ICI treatment is influenced by many factors, we selected the Fibrosheath interacting protein 2 (FSIP2) gene and systematically analyzed its potential to predict the efficacy of ICI treatment.

Methods

Patient data were collected from an ICI treatment cohort (n = 120) and a The Cancer Genome Atlas (TCGA)-SKCM cohort (n = 467). The data were divided into an FSIP2-mutant (MT) group and FSIP2-wild-type (WT) group according to FSIP2 mutation status. In this study, we analyzed the patients' overall survival rate, tumor mutational burden (TMB), neoantigen load (NAL), copy number variation (CNV), cell infiltration data and immune-related genes. We used gene set enrichment analysis (GSEA) to delineate biological pathways and processes associated with the efficacy of immunotherapy.

Results

The efficacy of ICI treatment of SKCM patients with FSIP2 mutation was significantly better than that of patients without FSIP2 mutation. The patients in the FSIP2-MT group had higher tumor immunogenicity and lower regulatory T cell (Treg) infiltration. Results of GSEA showed that pathways related to tumor progression (MAPK and FGFR), immunomodulation, and IL-2 synthesis inhibition were significantly downregulated in the FSIP2-MT group.

Conclusion

Our research suggests that the FSIP2 gene has the potential to predict the efficacy of ICI treatment. The high tumor immunogenicity and low Treg levels observed may be closely related to the fact that patients with FSIP2-MT can benefit from ICI treatment.

Cell-type-specific Modulation of Non-homologous End Joining of Gamma Ray-induced DNA Double-strand Breaks by cAMP Signaling in Human Cancer Cells

BACKGROUND

Cyclic AMP (cAMP) signaling is activated by various hormones and neurotransmitters and regulates numerous physiological phenomena, including energy metabolism, gene expression, and proliferation. cAMP signaling plays a role in the repair of DNA damage, but its specific function is inconsistent in the literature. The present study aimed to investigate the mechanism of the different roles of cAMP signaling in DNA repair by analyzing the cell-type differences in the modulation of DNA repair by cAMP signaling following γ-ray irradiation.

METHODS

cAMP signaling was activated in human malignant melanoma cells (SK-MEL-2 and SK-MEL-28), human uterine cervical cancer cells (HeLa and SiHa) and human non-small cell lung cancer cells (H1299 and A549) by expressing a constitutively active mutant of the long-form stimulatory α subunit of GTP-binding protein or by treating with isoproterenol and prostaglandin E2 before γ-ray irradiation. DNA damage was quantitated by western blot analysis of γ-H2AX, and non-homologous end joining (NHEJ) was assessed by fluorescent reporter plasmid repair assay and immunofluorescence of microscopic foci of XRCC4 and DNA-ligase IV.

RESULTS

cAMP signaling modulated DNA damage, apoptosis and the NHEJ repair following γ-ray irradiation differently depending upon the cell type. cAMP signaling regulated the phosphorylation of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) at Ser2056 and Thr2609 in cell-type-specific manners following γ-ray irradiation, an activity that was mediated by protein kinase A.

CONCLUSION

cAMP signaling modulates the NHEJ repair of γ-ray-induced DNA damage in melanoma cells, uterine cervical cancer cells and lung cancer cells in a cell-type-specific manner, and the modulation is likely mediated by protein kinase A-dependent phosphorylation of DNA-PKcs. This study suggests that cell- and tissue-specific modulation of DNA damage repair by cAMP signaling may contribute to improve the therapeutic efficiency of radiation therapy.

Inhibition of non-homologous end joining of gamma ray-induced DNA double-strand breaks by cAMP signaling in lung cancer cells

DNA double-strand breaks (DSB) are formed by various exogenous and endogenous factors and are repaired by homologous recombination and non-homologous end joining (NHEJ). DNA-dependent protein kinase (DNA-PK) is the principal enzyme for NHEJ. We explored the role and the underlying mechanism of cAMP signaling in the NHEJ repair of DSBs resulted from gamma ray irradiation to non-small cell lung cancer (NSLC) cells. Activated cAMP signaling by expression of an activated stimulatory GTP-binding protein or by pretreatment with isoproterenol and prostaglandin E2, delayed the repair of DSBs resulted from gamma ray irradiation, and the delaying effects depended on protein kinase A (PKA). Activated cAMP signaling suppressed XRCC4 and DNA ligase IV recruitment into DSB foci, and reduced phosphorylation at T2609 in DNA-PK catalytic subunit (DNA-PKcs) with a concomitant increase in phosphorylation at S2056 in PKA-dependent ways following gamma ray irradiation. cAMP signaling decreased phosphorylation of T2609 by protein phosphatase 2A-dependent inhibition of ATM. We conclude that cAMP signaling delays the repair of gamma ray-induced DNA DSBs in NSLC cells by inhibiting NHEJ via PKA-dependent pathways, and that cAMP signaling differentially modulates DNA-PKcs phosphorylation at S2056 and T2609, which might contribute to the inhibition of NHEJ in NSLC cells.

The diagnostic value of extracellular protein kinase A (ECPKA) in serum for gastric and colorectal cancer

Background

For the biomarkers of cancer, many chromosomal and genetic alterations have been examined as possible. However, some tumors do not display a clear molecular and genetic signature. While there are some cellular processes regulated by second messenger intracellular pathways indeed involved in carcinogenesis. The first intracellular second messenger was described as cyclic adenosine 3',5'-monophosphate (cAMP), and cAMP-dependent protein kinase (PKA) play a crucial role in several biological processes; The dysregulation of PKA-mediated signaling in several types of cancer should be investigated. More interesting, the alpha catalytic subunit of PKA (PKACα) could be secreted into the conditioned medium by different types of cancer cells, and it also existed in the serum of some cancer patients, defined as extracellular protein kinase A (ECPKA).

Methods

The levels of serum PKACα from healthy people, gastric cancer and colon cancer patients were detected by ELISA kits. Western blotting was used to detect the expression of PKACα in cancer tissue and the adjacent mucosa. Mann-Whitney test was applied to analyze the patients’ characteristics and serum PKACα. ROC analyses were performed to further evaluate the utility of PKACα in cancer diagnosis. The correlation of serum PKACα and T stage, age, and tumor markers were analyzed by Spearman rank and Pearson correlation analysis, respectively.

Results

There were significant differences of PKACα in serum between the volunteers and the gastric cancers (P<0.01), but not the colorectal cancers (P>0.05). ROC analyses evaluated the utility of PKACα for gastric cancer with 61.90% sensitivities and 87.50% specificities. The serum PKACα was correlated with tumor marker CA50, while there was no significant difference of PKACα expression between the gastric/colorectal cancer tissue and the adjacent mucosa.

Conclusions

The above results implied that PKACα levels might be a potential biomarker for the early screening of gastric cancers. Moreover, further research is still needed to investigate the role of secreted PKACα and the regulatory mechanism in tumor progression.

A perspective profile of ADCY1 in cAMP signaling with drug-resistance in lung cancer

Adenylate cyclase 1 (ADCY1 or AC1) is a member of ADCY superfamily and was primarily found to be expressed in the brain. ADCY1 is responsible for catalyzing ATP to cyclic AMP (cAMP). As a secondary messenger, cAMP can regulate plenty of cellular activities. cAMP can perform its regulation in cellular transport through the binding to cAMP dependent protein kinases (PKAs), cAMP-activated guanine exchange factors (EPACs) and cyclic nucleotide-gated channels functioning in transduction of sensory signals (CNGs). Lung cancer is one of the leading factors of cancer-related death worldwide. Platinum-based chemotherapy is the first-line treatment for advanced lung cancer patients. In addition, surgical treatment, radiation treatment, and molecular targeted therapy are also therapeutic options for lung cancer patients in clinical settings. However, drug resistance and toxicity are the major obstacles that affect chemotherapy outcome and prognosis of lung cancer patients. And the therapeutic efficiency and adverse effects are varying with each individual. In recent years, investigations based on genetic sequencing have revealed the emerging role of ADCY1 mutations in affecting drug efficiency in various cancers such as lung cancer, esophageal cancer and colorectal cancer. The potential function of ADCY1 in chemotherapy resistance is of great importance to be noticed and investigated.

Metabolic Regulation of Glycolysis and AMP Activated Protein Kinase Pathways during Black Raspberry-Mediated Oral Cancer Chemoprevention

Oral cancer is a public health problem with an incidence of almost 50,000 and a mortality of 10,000 each year in the USA alone. Black raspberries (BRBs) have been shown to inhibit oral carcinogenesis in several preclinical models, but our understanding of how BRB phytochemicals affect the metabolic pathways during oral carcinogenesis remains incomplete. We used a well-established rat oral cancer model to determine potential metabolic pathways impacted by BRBs during oral carcinogenesis. F344 rats were exposed to the oral carcinogen 4-nitroquinoline-1-oxide in drinking water for 14 weeks, then regular drinking water for six weeks. Carcinogen exposed rats were fed a 5% or 10% BRB supplemented diet or control diet for six weeks after carcinogen exposure. RNA-Seq transcriptome analysis on rat tongue, and mass spectrometry and NMR metabolomics analysis on rat urine were performed. We tentatively identified 57 differentially or uniquely expressed metabolites and over 662 modulated genes in rats being fed with BRB. Glycolysis and AMPK pathways were modulated during BRB-mediated oral cancer chemoprevention. Glycolytic enzymes Aldoa, Hk2, Tpi1, Pgam2, Pfkl, and Pkm2 as well as the PKA-AMPK pathway genes Prkaa2, Pde4a, Pde10a, Ywhag, and Crebbp were downregulated by BRBs during oral cancer chemoprevention. Furthermore, the glycolysis metabolite glucose-6-phosphate decreased in BRB-administered rats. Our data reveal the novel metabolic pathways modulated by BRB phytochemicals that can be targeted during the chemoprevention of oral cancer.

Biological and Toxicological Evaluation of N-(4methyl-phenyl)-4-methylphthalimide on Bone Cancer in Mice

BACKGROUND

It was recently demonstrated that the phthalimide N-(4-methyl-phenyl)-4- methylphthalimide (MPMPH-1) has important effects against acute and chronic pain in mice, with a mechanism of action correlated to adenylyl cyclase inhibition. Furthermore, it was also demonstrated that phthalimide derivatives presented antiproliferative and anti-tumor effects. Considering the literature data, the present study evaluated the effects of MPMPH-1 on breast cancer bone metastasis and correlated painful symptom, and provided additional toxicological information about the compound and its possible metabolites.

METHODS

In silico toxicological analysis was supported by in vitro and in vivo experiments to demonstrate the anti-tumor and anti-hypersensitivity effects of the compound.

RESULTS

The data obtained with the in silico toxicological analysis demonstrated that MPMPH-1 has mutagenic potential, with a low to moderate level of confidence. The mutagenicity potential was in vivo confirmed by micronucleus assay. MPMPH-1 treatments in the breast cancer bone metastasis model were able to prevent the osteoclastic resorption of bone matrix. Regarding cartilage, degradation was considerably reduced within the zoledronic acid group, while in MPMPH-1, chondrocyte multiplication was observed in random areas, suggesting bone regeneration. Additionally, the repeated treatment of mice with MPMPH-1 (10 mg/kg, i.p.), once a day for up to 36 days, significantly reduces the hypersensitivity in animals with breast cancer bone metastasis.

CONCLUSION

Together, the data herein obtained show that MPMPH-1 is relatively safe, and significantly control the cancer growth, allied to the reduction in bone reabsorption and stimulation of bone and cartilage regeneration. MPMPH-1 effects may be linked, at least in part, to the ability of the compound to interfere with adenylylcyclase pathway activation.

Protein Kinase A Distribution Differentiates Human Glioblastoma from Brain Tissue

Brain tumor glioblastoma has no clear molecular signature and there is no effective therapy. In rodents, the intracellular distribution of the cyclic AMP (cAMP)-dependent protein kinase (Protein kinase A, PKA) R2Alpha subunit was previously shown to differentiate tumor cells from healthy brain cells. Now, we aim to validate this observation in human tumors. The distribution of regulatory (R1 and R2) and catalytic subunits of PKA was examined via immunohistochemistry and Western blot in primary cell cultures and biopsies from 11 glioblastoma patients. Data were compared with information obtained from 17 other different tumor samples. The R1 subunit was clearly detectable only in some samples. The catalytic subunit was variably distributed in the different tumors. Similar to rodent tumors, all human glioblastoma specimens showed perinuclear R2 distribution in the Golgi area, while it was undetectable outside the tumor. To test the effect of targeting PKA as a therapeutic strategy, the intracellular cyclic AMP concentration was modulated with different agents in four human glioblastoma cell lines. A significant increase in cell death was detected after increasing cAMP levels or modulating PKA activity. These data raise the possibility of targeting the PKA intracellular pathway for the development of diagnostic and/or therapeutic tools for human glioblastoma.

Linking tumor glycolysis and immune evasion in cancer: Emerging concepts and therapeutic opportunities

Metabolic reprogramming and immune evasion are two hallmarks of cancer. Metabolic reprogramming is exemplified by cancer's propensity to utilize glucose at an exponential rate which in turn is linked with "aerobic glycolysis", popularly known as the "Warburg effect". Tumor glycolysis is pivotal for the efficient management of cellular bioenergetics and uninterrupted cancer growth. Mounting evidence suggests that tumor glycolysis also plays a key role in instigating immunosuppressive networks that are critical for cancer cells to escape immune surveillance ("immune evasion"). Recent data show that induction of cellular stress or metabolic dysregulation sensitize cancer cells to antitumor immune cells implying that metabolic reprogramming and immune evasion harmonize during cancer progression. However, the molecular link between these two hallmarks of cancer remains obscure. In this review the molecular intricacies of tumor glycolysis that facilitate immune evasion has been discussed in the light of recent research to explore immunotherapeutic potential of targeting cancer metabolism.