Overexpression of zinc-finger protein 777 (ZNF777) inhibits proliferation at low cell density through down-regulation of FAM129A

ZNF862 induces cytostasis and apoptosis via the p21-RB1 and Bcl-xL-Caspase 3 signaling pathways in human gingival fibroblasts

OBJECTIVE

This study investigates the effects of ZNF862 on the proliferation and apoptosis of human gingival fibroblasts and their related mechanisms.

BACKGROUND

As a major transcription factor family, zinc finger proteins (ZFPs) regulate cell differentiation, growth, and apoptosis through their conserved zinc finger motifs, which allow high flexibility and specificity in gene regulation. In our previous study, ZNF862 mutation was associated with hereditary gingival fibromatosis. Nevertheless, little is known about the biological function of ZNF862. Therefore, this study was aimed to reveal intracellular localization of ZNF862, the influence of ZNF862 on the growth and apoptosis of human gingival fibroblasts (HGFs) and its potential related mechanisms.

METHODS

Immunohistochemistry, immunofluorescence staining, and western blotting were performed to determine the intracellular localization of ZNF862 in HGFs. HGFs were divided into three groups: ZNF862 overexpression group, ZNF862 interference group, and the empty vector control group. Then, the effects of ZNF862 on cell proliferation, migration, cell cycle, and apoptosis were evaluated. qRT-PCR and western blotting were performed to further explore the mechanism related to the proliferation and apoptosis of HGFs.

RESULTS

ZNF862 was found to be localized in the cytoplasm of HGFs. In vitro experiments revealed that ZNF862 overexpression inhibited HGFs proliferation and migration, induced cell cycle arrest at the G0/G1-phase and apoptosis. Whereas, ZNF862 knockdown promoted HGFs proliferation and migration, accelerated the transition from the G0/G1 phase into the S and G2/M phase and inhibited cell apoptosis. Mechanistically, the effects of ZNF862 on HGFs proliferation and apoptosis were noted to be dependent on inhibiting the cyclin-dependent kinase inhibitor 1A (p21)-retinoblastoma 1 (RB1) signaling pathway and enhancing the B-cell lymphoma-extra-large (Bcl-xL)-Caspase 3 signaling pathway.

CONCLUSION

Our results for the first time reveal that ZNF862 is localized in the cytoplasm of HGFs. ZNF862 can inhibit the proliferation of HGFs by inhibiting the p21-RB1 signaling pathway, and it also promotes the apoptosis of HGFs by enhancing the Bcl-xL-Caspase 3 signaling pathway.

Eph signal inhibition potentiates the growth-inhibitory effects of PLK1 inhibition toward cancer cells

Anti-mitotic drugs are clinically used as anti-cancer treatments. Polo-like kinase 1 (PLK1) is a promising target against cancer cell division due to its importance in the whole process of mitosis, and thus PLK1-targeting agents have been developed in the last few decades. Clinical trial studies show that several PLK1 inhibitors are generally well-tolerated. However, the response rates are limited; therefore, it is needed to improve the efficacy of those drugs. Here, we show that NVP-BHG712, an erythropoietin-producing human hepatocellular (Eph) signaling inhibitor, potentiates the growth-inhibitory effects of the PLK1 inhibitors BI2536 and BI6727 in cancer cells. This combination treatment strongly suppresses cancer spheroid formation. Moreover, the combination drastically arrests cells at mitosis by continuous activation of the spindle assembly checkpoint (SAC), thereby inducing apoptosis. SAC activation caused by the combination of NVP-BHG712 and BI2536 is due to the inhibition of centrosome maturation and separation. Although the inactivation level of the PLK1 kinase is comparable between BI2536 treatment alone and combination treatment, the combination treatment strongly inactivates MAPK signaling in mitosis. Since inhibition of MAPK signaling potentiates the efficacy of BI2536 treatment, inactivation of PLK1 kinase and MAPK signaling contributes to the strong inhibition of centrosome separation. These results suggest that Eph signal inhibition potentiates the effect of PLK1 inhibition, leading to strong mitotic arrest via SAC activation and the subsequent reduction of cancer cell survival. The combination of PLK1 inhibition and Eph signal inhibition will provide a new effective strategy for targeting cancer cell division.

SH2D4A promotes centrosome maturation to support spindle microtubule formation and mitotic progression

Mitotic progression requires the precise formation of spindle microtubules based on mature centrosomes. During the G2/M transition, centrosome maturation progresses, and associated microtubules bundle to form mitotic spindle fibers and capture the chromosomes for alignment at the cell equator. Mitotic kinases-induced phosphorylation signaling is necessary for these processes. Here, we identified SH2 domain-containing protein 4A (SH2D4A/PPP1R38) as a new mitotic regulator. SH2D4A knockdown delays mitotic progression. The time-lapse imaging analysis showed that SH2D4A specifically contributes to the alignment of chromosomes. The cold treatment assay and microtubule regrowth assay indicated that SH2D4A promotes microtubule nucleation to support kinetochore-microtubule attachment. This may be due to the centrosome maturation by SH2D4A via centrosomal recruitment of pericentriolar material (PCM) such as cep192, γ-tubulin, and PLK1. SH2D4A was found to be a negative regulator of PP1 phosphatase. Consistently, treatment with a PP1 inhibitor rescues SH2D4A-knockdown-induced phenotypes, including the microtubule nucleation and centrosomal recruitment of active PLK1. These results suggest that SH2D4A is involved in PCM recruitment to centrosomes and centrosome maturation through attenuation of PP1 phosphatases, accelerating the spindle formation and supporting mitotic progression.

Genome-wide assessment of DNA methylation alterations induced by superovulation, sexual immaturity and in vitro follicle growth in mouse blastocysts

BACKGROUND

In their attempt to fulfill the wish of having children, women who suffer from fertility issues often undergo assisted reproductive technologies such as ovarian stimulation, which has been associated with adverse health outcomes and imprinting disorders in children. However, given the crucial role of exogenous hormone stimulation in improving human infertility treatments, a more comprehensive analysis of the potential impacts on DNA methylation in embryos following ovarian stimulation is needed. Here, we provide genome-wide DNA methylation profiles of blastocysts generated after superovulation of prepubertal or adult mice, compared with blastocysts derived from non-stimulated adult mice. Additionally, we assessed the impact of the in vitro growth and maturation of oocytes on methylation in blastocysts.

RESULTS

Neither hormone stimulation nor sexual maturity had an impact on the low global methylation levels characteristic of the blastocyst stage or was associated with extensive DNA methylation alterations. However, we found hormone- and age-associated changes at specific positions but dispersed throughout the genome. In particular, we detected anomalous methylation at a limited number of CpG islands. Additionally, superovulation in adult mice was associated with alterations at the Sgce and Zfp777 imprinted genes. On the other hand, in vitro culture of follicles from the early pre-antral stage was associated with globally reduced methylation and increased variability at imprinted loci in blastocysts.

CONCLUSIONS

Our results indicate a minimal effect of ovarian stimulation of adult and prepubertal mice on the DNA methylation landscape attained at the blastocyst stage, but potentially greater impacts of in vitro growth and maturation of oocytes. These findings have potential significance for the improvement of assisted reproductive techniques, in particular for those related to treatments in prepubertal females, which could be crucial for improving human fertility preservation strategies.

NIBAN1, Exploring its Roles in Cell Survival Under Stress Context

Cell survival must quickly activate specific mechanisms that enable to detect changes in the cellular microenvironment. The impact of these cell alteration has direct consequences on cellular homeostasis. Cellular stress, as well as its regulation and implication, has been studied in different pathologies. In this sense, the alteration in NIBAN1 expression seems to act in response to different cellular disturbances. Over the years, the knowledge of NIBAN1 functions has improved, demonstrating its important cell roles, favoring the cell survival under stress context. In response to the disturbances, NIBAN1 seems to be involved in the decision-making process between cell survival and death. The increase in NIBAN1 expression has been related to cellular mechanisms that seek to minimize the damage caused to cellular homeostasis. In this review, the main biological insights attributed to the NIBAN1 gene in different cellular contexts and its role as a mediator of cellular stress are discussed.

CBFβ promotes colorectal cancer progression through transcriptionally activating OPN, FAM129A, and UPP1 in a RUNX2-dependent manner

Colorectal cancer (CRC) is commonly associated with aberrant transcription regulation, but characteristics of the dysregulated transcription factors in CRC pathogenesis remain to be elucidated. In the present study, core-binding factor β (CBFβ) is found to be significantly upregulated in human CRC tissues and correlates with poor survival rate of CRC patients. Mechanistically, CBFβ is found to promote CRC cell proliferation, migration, invasion, and inhibit cell apoptosis in a RUNX2-dependent way. Transcriptome studies reveal that CBFβ and RUNX2 form a transcriptional complex that activates gene expression of OPN, FAM129A, and UPP1. Furthermore, CBFβ significantly promotes CRC tumor growth and live metastasis in a mouse xenograft model and a mouse liver metastasis model. In addition, tumor-suppressive miR-143/145 are found to inhibit CBFβ expression by specifically targeting its 3'-UTR region. Consistently, an inverse correlation between miR-143/miR-145 and CBFβ expression levels is present in CRC patients. Taken together, this study uncovers a novel regulatory role of CBFβ-RUNX2 complex in the transcriptional activation of OPN, FAM129A, and UPP1 during CRC development, and may provide important insights into CRC pathogenesis.

[Novel Tyrosine Phosphorylation Signals in the Nucleus and on Mitotic Spindle Fibers and Lysosomes Revealed by Strong Inhibition of Tyrosine Dephosphorylation]

Protein-tyrosine phosphorylation is one of the posttranslational modifications and plays critical roles in regulating a wide variety of cellular processes, such as cell proliferation, differentiation, adhesion, migration, survival, and apoptosis. Protein-tyrosine phosphorylation is reversibly regulated by protein-tyrosine kinases and protein-tyrosine phosphatases. Strong inhibition of protein-tyrosine phosphatase activities is required to undoubtedly detect tyrosine phosphorylation. Our extremely careful usage of Na₃VO₄, a potent protein-tyrosine phosphatase inhibitor, has revealed not only the different intracellular trafficking pathways of Src-family tyrosine kinase members but also novel tyrosine phosphorylation signals in the nucleus and on mitotic spindle fibers and lysosomes. Furthermore, despite that the first identified oncogene product v-Src is generally believed to induce transformation through continuous stimulation of proliferation signaling by its strong tyrosine kinase activity, v-Src-driven transformation was found to be caused not by continuous proliferation signaling but by v-Src tyrosine kinase activity-dependent stochastic genome alterations. Here, I summarize our findings regarding novel tyrosine phosphorylation signaling in a spatiotemporal sense and highlight the significance of the roles of tyrosine phosphorylation in transcriptional regulation inside the nucleus and chromosome dynamics.

Differential microRNA Expression in Newcastle Disease Virus-Infected HeLa Cells and Its Role in Regulating Virus Replication

As an oncolytic virus, Newcastle disease virus (NDV) can specifically kill tumor cells and has been tested as an attractive oncolytic agent for cancer virotherapy. Virus infection can trigger the changes of the cellular microRNA (miRNA) expression profile, which can greatly influence viral replication and pathogenesis. However, the interplay between NDV replication and cellular miRNA expression in tumor cells is still largely unknown. In the present study, we compared the profiles of cellular miRNAs in uninfected and NDV-infected HeLa cells by small RNA deep sequencing. Here we report that NDV infection in HeLa cells significantly changed the levels of 40 miRNAs at 6 h post-infection (hpi) and 62 miRNAs at 12 hpi. Among 23 highly differentially expressed miRNAs, NDV infection greatly promoted the levels of 3 miRNAs and suppressed the levels of 20 miRNAs at both time points. These 23 miRNAs are predicted to target various genes involved in virus replication and antiviral immunity such as ErbB, Jak-STAT, NF-kB and RIG-I-like receptor. Verification of deep sequencing results by quantitative RT-PCR showed that 9 out of 10 randomly selected miRNAs chosen from this 23-miRNA pool were consistent with deep sequencing data, including 6 down-regulated and 3 up-regulated. Further functional research revealed that hsa-miR-4521, a constituent in this 23-miRNA pool, inhibited NDV replication in HeLa cells. Moreover, dual-luciferase and gene expression array uncovered that the member A of family with sequence similarity 129 (FAM129A) was directly targeted by hsa-miR-4521 and positively regulated NDV replication in HeLa cells, indicating that hsa-miR-4521 may regulate NDV replication via interaction with FAM129A. To our knowledge, this is the first report of the dynamic cellular miRNA expression profile in tumor cells after NDV infection and may provide a valuable basis for further investigation on the roles of miRNAs in NDV-mediated oncolysis.

A cell permeant phosphopeptide mimetic of Niban inhibits p38 MAPK and restores endothelial function after injury

Vascular injury leads to membrane disruption, ATP release, and endothelial dysfunction. Increases in the phosphorylation of p38 mitogen‐activated protein kinase (p38 MAPK) and decreases in the phosphorylation of Niban, a protein implicated in ER stress and apoptosis, are associated with vascular injury. A cell permeant phosphopeptide mimetic of Niban (NiPp) was generated. The effects of NiPp in restoring endothelial function were determined ex vivo using intact rat aortic tissue (RA) after pharmacological activation of p38 MAPK and also in multiple clinically relevant injury models. Anisomycin (Aniso) increased p38 MAPK phosphorylation and reduced endothelial‐dependent relaxation in RA. Treatment with NiPp prevented Ansio‐induced reduction in endothelial function and increases in p38 MAPK phosphorylation. NiPp treatment also restored endothelial function after stretch injury (subfailure stretch), treatment with acidic Normal Saline (NS), and P2X7R activation with 2′(3′)‐O‐(4‐Benzoylbenzoyl)adenosine 5′‐triphosphate (BzATP). Aged, diseased, human saphenous vein (HSV) remnants obtained from patients undergoing coronary bypass surgical procedures have impaired endothelial function. Treatment of these HSV segments with NiPp improved endothelial‐dependent relaxation. Kinome screening experiments indicated that NiPp inhibits p38 MAPK. These data demonstrate that p38 MAPK and Niban signaling have a role in endothelial function, particularly in response to injury. Niban may represent an endogenous regulator of p38 MAPK activation. The NiPp peptide may serve as an experimental tool to further elucidate p38 MAPK regulation and as a potential therapeutic for endothelial dysfunction.

Zinc Finger Protein 521, Negatively Regulated by MicroRNA-204-5p, Promotes Proliferation, Motility and Invasion of Gastric Cancer Cells

OBJECTIVE

This study aims to investigate the expression, role, and detailed mechanism of microRNA-204-5p and zinc finger protein 521 in gastric cancer.

METHODS

Immunohistochemistry was adopted to detect the expressions of zinc finger protein 521 in 82 cases of gastric cancer tissues. Western blot was used to detect the expressions of zinc finger protein 521 in gastric cancer cells and adjacent cells. Moreover, the correlation between zinc finger protein 521 and the prognosis of patients were also evaluated. Cell Counting Kit 8 assay and colony formation assay were performed to figure out the impact of zinc finger protein 521 on the proliferation of gastric cancer cells. By conducting flow cytometry, the effect of zinc finger protein 521 on the apoptosis of gastric cancer cells was determined. The scratch wound healing assay and transwell invasion assay were carried out to determine the effect of zinc finger protein 521 on regulating the motility and invasion of gastric cancer cells. Ultimately, the targeting relationship and interaction between microRNA-204-5p and zinc finger protein 521 were verified by real-time polymerase chain reaction, Western blot, and dual luciferase reporter gene assay.

RESULTS

Compared with adjacent cells, zinc finger protein 521 was highly expressed in gastric cancer cells, which was related to TNM stage (P = .0388), tumor size (P = .0168), and local lymph node metastasis (P = .0024). Overexpressed zinc finger protein 521 can promote the proliferation, migration, and invasion of gastric cancer cells and inhibit the apoptosis. Zinc finger protein 521 is a target gene of microRNA-106-5p, and there was a negative correlation between the expression of zinc finger protein 521 and microRNA-204-5p.

CONCLUSION

Zinc finger protein 521 can arrest the apoptosis and enhance the proliferation, migration, and invasion of gastric cancer cells via regulating microRNA-204-5p. Our study may provide novel clues for the treatment of patients with gastric cancer.

DUF3669, a "domain of unknown function" within ZNF746 and ZNF777, oligomerizes and contributes to transcriptional repression

Background

ZNF746 and ZNF777 belong to a subset of the large Krüppel-associated box (KRAB) zinc finger (ZNF) transcription factor family. They contain, like four other members in human, an additional conserved domain, the “domain of unknown function 3669” (DUF3669). Previous work on members of this subfamily suggested involvement in transcriptional regulation and aberrant ZNF746 overexpression leads to neuronal cell death in Parkinson’s disease.

Results

Here we demonstrate that N-terminal protein segments of the ZNF746a major isoform and ZNF777 act in concert to exert moderate transcriptional repression activities. Full potency depended on the intact configuration consisting of DUF3669, a variant KRAB domain and adjacent sequences. While DUF3669 contributes an intrinsic weak inhibitory activity, the isolated KRAB-AB domains did not repress. Importantly, DUF3669 provides a novel protein-protein interaction interface and mediates direct physical interaction between the members of the subfamily in oligomers. The ZNF746 protein segment encoded by exons 5 and 6 boosted repressor potency, potentially due to the presence of an acceptor lysine for sumoylation at K189. Repressor activity of the potent canonical ZNF10 KRAB domain was not augmented by heterologous transfer of DUF3669, pointing to the importance of context for DUF3669’s impact on transcription. Neither ZNF746a nor ZNF777 protein segments stably associated with TRIM28 within cells. Isoform ZNF746b that contains, unlike the major isoform, a full-length KRAB-A subdomain, displayed substantially increased repressor potency. This increase is due to canonical mechanisms known for KRAB domains since it did not take place in HAP1 knockout models of TRIM28 and SETDB1. A glycine to glutamic acid replacement that complies with a bona fide conserved “MLE” sequence within KRAB-A led to a further strong gain in repressor potency to levels comparable to those of the canonical ZNF10 KRAB domain. Each gain of repressive activity was accompanied by an enhanced interaction with TRIM28 protein.

Conclusion

DUF3669 adds a protein-protein interaction surface to a subgroup of KRAB-ZNF proteins within an N-terminal configuration with variant KRAB and adjacent sequences likely regulated by sumoylation. DUF3669 contributes to transcriptional repression strength and its homo- and hetero-oligomerization characteristics probably extended the regulatory repertoire of KRAB-ZNF transcription factors during amniote evolution.

miR-135a deficiency inhibits the AR42J cells damage in cerulein-induced acute pancreatitis through targeting FAM129A

Acute pancreatitis (AP) is a common clinical critical disease with high mortality and the exact pathogenesis is not fully elucidated. The present study aimed to uncover the function of miR-135a in the proliferation, apoptosis, and inflammatory characteristics of diseased pancreatic cells and the potential molecular mechanisms. The expression patterns of miR-135a and family with sequence similarity 129 member A (FAM129A) in patients with AP were analyzed on the basis of the GEO database. The transfection efficiency and expression level of miR-135a in AR42J cells were determined by qRT-PCR. The biological characteristics of AR42J cells treated with cerulein were detected by cell counting kit-8 (CCK-8), flow cytometry, and western blot assays. The potential interaction between miR-135a and FAM129A was confirmed by bioinformatics prediction softwares and luciferase reporter assay. MiR-135a inhibitor and pcDNA3.1-FAM129A were co-transfected to determine the regulation of miR-135a/FAM129A on inflammatory AR42J cell injury. We observed that miR-135a was highly expressed in AP samples. Depletion of miR-135a could alleviate the condition so that the AR42J cells proliferation increased, apoptosis decreased, and the expression of inflammatory cytokines enhanced. In addition, mRNA and protein expression of FAM129A were negatively regulated by miR-135a, and over-expression of FAM129A could strengthen the relief effect of miR-135a inhibitor in AP induced by cerulein. In summary, our data demonstrates that silencing miR-135a reduces AR42J cells injury and inflammatory response in AP induced by cerulein through targeting FAM129A.

Niban protein regulates apoptosis in HK-2 cells via caspase-dependent pathway

Purpose: To investigate whether Niban protein plays a role in renal interstitial fibrosis by regulating renal tubular epithelial cell apoptosis and explore the underlying mechanism. Methods: Unilateral ureteral obstruction (UUO) model was performed in C57B/6J mice, and divided into sham operation group and groups of days 3, days 7, and days 14. Niban expression was detected by immunohistochemistry and Western blot. TUNEL assays were used to detected apoptosis. Niban siRNA and overexpression Niban plasmid were transfected in HK-2 cells respectively to explore apoptosis related mechanisms of Niban during angiotensin II (AngII) - and endoplasmic reticulum (ER) stress-induced injury. Results: With the development of obstruction, Niban's expression decreased gradually while apoptosis increased. Silencing of Niban not only increased the AngII- and ER stress-induced apoptosis, but also promoted the expression of caspase 8, caspase 9, Bip, and Chop. Overexpression of Niban reduced AngII-induced apoptosis and the expression of caspase 8 and caspase 9. Conclusions: Niban protein is involved in apoptosis regulation in HK-2 cells, and most likely via caspase-dependent pathway.

Desuppression of TGF-β signaling via nuclear c-Abl-mediated phosphorylation of TIF1γ/TRIM33 at Tyr-524, -610, and -1048

Protein-tyrosine kinases regulate a broad range of intracellular processes occurring primarily just beneath the plasma membrane. With the greatest care to prevent dephosphorylation, we have shown that nuclear tyrosine phosphorylation regulates global chromatin structural states. However, the roles for tyrosine phosphorylation in the nucleus are poorly understood. Here we identify transcriptional intermediary factor 1-γ (TIF1γ/TRIM33/Ectodermin), which suppresses transforming growth factor-β (TGF-β) signaling through the association with Smad2/3 transcription factor, as a new nuclear substrate of c-Abl tyrosine kinase. Replacement of the three tyrosine residues Tyr-524, -610, and -1048 with phenylalanine (3YF) inhibits c-Abl-mediated phosphorylation of TIF1γ and enhances TIF1γ's association with Smad3. Importantly, knockdown-rescue experiments show that 3YF strengthens TIF1γ's ability to suppress TGF-β signaling. Intriguingly, activation of c-Abl by epidermal growth factor (EGF) induces desuppression of TGF-β signaling via enhancing the tyrosine phosphorylation level of TIF1γ. TGF-β together with EGF synergistically provokes desuppressive responses of epithelial-to-mesenchymal transition through tyrosine phosphorylation of TIF1γ. These results suggest that nuclear c-Abl-mediated tyrosine phosphorylation of TIF1γ has a desuppressive role in TGF-β-Smad2/3 signaling.

Src Acts as an Effector for Ku70-dependent Suppression of Apoptosis through Phosphorylation of Ku70 at Tyr-530

Src-family tyrosine kinases are widely expressed in many cell types and participate in a variety of signal transduction pathways. Despite the significance of Src in suppression of apoptosis, its mechanism remains poorly understood. Here we show that Src acts as an effector for Ku70-dependent suppression of apoptosis. Inhibition of endogenous Src activity promotes UV-induced apoptosis, which is impaired by Ku70 knockdown. Src phosphorylates Ku70 at Tyr-530, being close to the possible acetylation sites involved in promotion of apoptosis. Src-mediated phosphorylation of Ku70 at Tyr-530 decreases acetylation of Ku70, whereas Src inhibition augments acetylation of Ku70. Importantly, knockdown-rescue experiments with stable Ku70 knockdown cells show that the nonphosphorylatable Y530F mutant of Ku70 reduces the ability of Ku70 to suppress apoptosis accompanied by augmentation of Ku70 acetylation. Our results reveal that Src plays a protective role against hyperactive apoptotic cell death by reducing apoptotic susceptibility through phosphorylation of Ku70 at Tyr-530.

The possible roles of B-cell novel protein-1 (BCNP1) in cellular signalling pathways and in cancer

B‐cell novel protein‐1 (BCNP1) or Family member of 129C (FAM129C) was identified as a B‐cell‐specific plasma‐membrane protein. Bioinformatics analysis predicted that BCNP1 might be heavily phosphorylated. The BCNP1 protein contains a pleckstrin homology (PH) domain, two proline‐rich (PR) regions and a Leucine Zipper (LZ) domain suggesting that it may be involved in protein‐protein interactions. Using The Cancer Genome Atlas (TCGA) data sets, we investigated the correlation of alteration of the BCNP1 copy‐number changes and mutations in several cancer types. We also investigated the function of BCNP1 in cellular signalling pathways. We found that BCNP1 is highly altered in some types of cancers and that BCNP1 copy‐number changes and mutations co‐occur with other molecular alteration events for TP53 (tumour protein P53), PIK3CA (Phosphatidylinositol‐4,5‐Bisphosphate 3‐Kinase, Catalytic Subunit Alpha), MAPK1 (mitogen‐activated protein kinase‐1; ERK: extracellular signal regulated kinase), KRAS (Kirsten rat sarcoma viral oncogene homolog) and AKT2 (V‐Akt Murine Thymoma Viral Oncogene Homolog 2). We also found that PI3K (Phoshoinositide 3‐kinase) inhibition and p38 MAPK (p38 mitogen‐activated protein kinase) activation leads to reduction in phosphorylation of BCNP1 at serine residues, suggesting that BCNP1 phosphorylation is PI3K and p38MAPK dependent and that it might be involved in cancer. Its degradation depends on a proteasome‐mediated pathway.

Role for Tyrosine Phosphorylation of A-kinase Anchoring Protein 8 (AKAP8) in Its Dissociation from Chromatin and the Nuclear Matrix

Protein-tyrosine phosphorylation regulates a wide variety of cellular processes at the plasma membrane. Recently, we showed that nuclear tyrosine kinases induce global nuclear structure changes, which we called chromatin structural changes. However, the mechanisms are not fully understood. In this study we identify protein kinase A anchoring protein 8 (AKAP8/AKAP95), which associates with chromatin and the nuclear matrix, as a nuclear tyrosine-phosphorylated protein. Tyrosine phosphorylation of AKAP8 is induced by several tyrosine kinases, such as Src, Fyn, and c-Abl but not Syk. Nucleus-targeted Lyn and c-Src strongly dissociate AKAP8 from chromatin and the nuclear matrix in a kinase activity-dependent manner. The levels of tyrosine phosphorylation of AKAP8 are decreased by substitution of multiple tyrosine residues on AKAP8 into phenylalanine. Importantly, the phenylalanine mutations of AKAP8 inhibit its dissociation from nuclear structures, suggesting that the association/dissociation of AKAP8 with/from nuclear structures is regulated by its tyrosine phosphorylation. Furthermore, the phenylalanine mutations of AKAP8 suppress the levels of nuclear tyrosine kinase-induced chromatin structural changes. In contrast, AKAP8 knockdown increases the levels of chromatin structural changes. Intriguingly, stimulation with hydrogen peroxide induces chromatin structural changes accompanied by the dissociation of AKAP8 from nuclear structures. These results suggest that AKAP8 is involved in the regulation of chromatin structural changes through nuclear tyrosine phosphorylation.