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REGγ is a proteasome activator that facilitates the degradation of small peptides. Abnormally high expression of REGγ has been observed in thyroid carcinomas. The purpose of the present study was to explore the role of REGγ in poorly differentiated thyroid carcinoma (PDTC). For this purpose, small interfering RNA (siRNA) was introduced to down-regulate the level of REGγ in the PDTC cell line SW579. Down-regulation of REGγ at the mRNA and protein levels was confirmed by RT-PCR and Western blot analyses. FACS analysis revealed cell cycle arrest at the G1/S transition, the MTT assay showed inhibition of cell proliferation, and the Transwell assay showed restricted cell invasion. Furthermore, the expression of the p21 protein was increased, the expression of proliferating cell nuclear antigen (PCNA) protein decreased, and the expression of the p27 protein was unchanged as shown by Western blot analyses. REGγ plays a critical role in the cell cycle, proliferation and invasion of SW579 cells. The alteration of p21 and PCNA proteins related to the down-regulation of REGγ suggests that p21 and PCNA participate in the process of REGγ regulation of cell cycle progression and cell proliferation. Thus, targeting REGγ has a therapeutic potential in the management of PDTC patients.

Acute promyelocytic leukemia (APL) is a special subtype of acute myeloid leukemia that responds to treatment with all-trans retinoic acid and arsenic trioxide. However, severe side effects and drug resistance limit the effectiveness of these treatments. Hence, new drugs for APL are required urgently. Shikonin, an active naphthoquinone derived from the Chinese medical herb Zi Cao exerts antitumor activity in several cancers. In the present study, the effects of shikonin on proliferation and apoptosis in NB4 cells, as well as related mechanisms were assessed. Treatment of NB4 cells with shikonin inhibited proliferation in a concentration- and time-dependent manner. The cell cycle was arrested in the G1 phase. NB4 cells treated with shikonin exhibited more apoptosis and higher levels of cleaved caspase-3 and poly ADP-ribose polymerase than control cells. Western blotting results demonstrated that the expression of p-p38 mitogen-activated protein kinase (p-p38MAPK) and p-c-Jun N-terminal kinase (p-JNK) was increased significantly by shikonin treatment, while the expression of p-ERK and c-Myc was decreased. In summary, these findings indicated that shikonin inhibited cell proliferation and induced apoptosis partly through modulation of the MAPKs and downregulation of c-Myc.

Background: Yes-associated protein (YAP), the nuclear effector of the Hippo pathway, is a candidate oncoprotein and participates in the progression of various malignancies. However, few reports have examined the effect of YAP inhibition in human leukemia HL-60 cells.Methods: We examined the effects of YAP knockdown or inhibition using short hairpin RNA (shRNA) or verteporfin (VP), respectively. Western blot assays were used to determine the expression levels of YAP, Survivin, cyclinD1, PARP, Bcl-2, and Bax. Cell proliferation was assessed using the cell counting kit (CCK-8) assay. Cell cycle progression and apoptosis were evaluated by flow cytometry, and apoptotic cell morphology was observed by Hoechst 33342 staining.Results: Knockdown or inhibition of YAP led to cell cycle arrest at the G0/G1 phase and increased apoptosis, inhibited cell proliferation, increased levels of Bax and cleaved PARP, and decreased levels of PARP, Bcl-2, Survivin, and cyclinD1. Moreover, Hoechst 33342 staining revealed increased cell nuclear fragmentation.Conclusion: Collectively, these results show that inhibition of YAP inhibits proliferation and induces apoptosis in HL-60 cells. Therefore, a novel treatment regime involving genetic or pharmacological inhibition of YAP could be established for acute promyelocytic leukemia.

Background and Aims: Verteporfin (VP), clinically used in photodynamic therapy for neovascular macular degeneration, has recently been proven a suppressor of yes-associated protein (YAP) and has shown potential in anticancer treatment. However, its anti-human leukemia effects in NB4 cells remain unclear. In this study, we investigated the effects of VP on proliferation and apoptosis in human leukemia NB4 cells.Methods: NB4 cells were treated with VP for 24 h. The effects of VP on cell proliferation were determined using a Cell-Counting Kit-8 assay (CCK-8) assay and colony forming assay. Apoptosis and cell cycle were evaluated by flow cytometry (FCM). The protein levels were detected by western blot.Results: We found that VP inhibited the proliferation of NB4 cells in a concentration and time-dependent manner. FCM analysis showed that VP induced apoptosis in a concentration dependent manner and that VP treatment led to cell cycle arrest at G0/G1 phase. Moreover, VP significantly decreased the protein expression of YAP, p-YAP, Survivin, c-Myc, cyclinD1, p-ERK, and p-AKT. In addition, VP increased the protein expression of cleaved caspase3, cleaved PARP, Bax, and p-p38 MAPK.Conclusions: VP inhibited the proliferation and induced apoptosis in NB4 cells.

Abstract. Acute promyelocytic leukemia (APL) is characterized by a specific chromosomal translation, resulting in a fusion gene that affects the differentiation, proliferation and apoptosis of APL cells. Epigallocatechin-3-gallate (EGCG), a catechin, exhibits numerous biological functions, including antitumor activities. Previous studies have reported that EGCG induces apoptosis in NB4 cells. However, the molecular mechanism underlying EGCG-induced apoptosis remains unclear. The present study aimed to determine the molecular basis of EGCG-induced apoptosis in NB4 cells. EGCG treatment significantly inhibited the viability of NB4 cells in a dose-dependent manner. In addition, EGCG treatment induced apoptosis and increased the levels of (Bcl-2-like protein 4) Bax protein expression. Moreover, EGCG treatment was able to increase phosphorylated (p)-p38α mitogen-activated protein kinase (MAPK) and Src homology 1 domain-containing protein tyrosine phosphatase (SHP-1) expression. Pretreatment with PD169316 (a p38 MAPK inhibitor) partially blocked EGCG-induced apoptosis and inhibited EGCG-mediated Bax expression. Similarly, pretreatment with NSC87877, an inhibitor of SHP-1, partially blocked EGCG-induced apoptosis and inhibited EGCG-mediated increases in p-p38α MAPK and Bax expression. Therefore, the results of the present study indicate that EGCG is able to induce apoptosis in NB4 cells via the SHP-1-p38αMAPK-Bax cascade. IntroductionAcute promyelocytic leukemia (APL), a unique subtype of acute myeloid leukemia, is characterized by a translocation between chromosomes 15 and 17 that encodes the oncogenic fusion protein promyelocytic leukemia/retinoic acid receptor-α (PML/RARα) (1). PML-RARα has an essential role in the development of APL by interfering with target genes that control differentiation, proliferation and apoptosis of APL cells (2). Considerable success in treating APL has been achieved using all-trans retinoic acid (3) and arsenic trioxide (4) in clinical settings. However, the toxicity of these molecules and the prevalence of drug-resistant forms of APL limit the clinical application of these drugs (5). Therefore, novel therapeutics to treat APL are urgently required.Src homology 1 domain-containing protein tyrosine phosphatase (SHP-1), also known as PTPN6 (6), consists of 17 exons and 16 introns and spans ~17 kb (7). SHP-1 controls the changes in the levels of intracellular phosphorylation, including JAK/STAT (8). SHP-1 exerts multiple biological functions through the alteration of several signaling pathways (9,10). A number of agonists and inhibitors of SHP-1 have been applied in clinical cancer therapies. For example, γ-tocotrienol (11) and regorafenib (12) have been used to treat breast tumors and colorectal cancer, respectively. Studies have reported that SHP-1 is highly expressed in normal hematopoietic cells (13) but weakly expressed in hematological malignancies, including Burkitt's lymphoma (14), APL (15) and chronic myeloid leukemia (16). Therefore, the present authors hypothesize that increases ...

Acute promyelocytic leukemia (APL) is a distinctive subtype of acute myeloid leukemia (AML) in which the hybrid protein promyelocytic leukemia protein/retinoic acid receptor α (PML/RARα) acts as a transcriptional repressor impairing the expression of genes that are critical to myeloid cell mutation. We aimed at explaining the molecular mechanism of green tea polyphenol epigallocatechin-3-gallate (EGCG) enhancement of ATRA-induced APL cell line differentiation. Tumor suppressor phosphatase and tensin homolog (PTEN) was found downregulated in NB4 cells and rescued by proteases inhibitor MG132. A significant increase of PTEN levels was found in NB4, HL-60 and THP-1 cells upon ATRA combined with EGCG treatment, paralleled by increased myeloid differentiation marker CD11b. EGCG in synergy with ATRA promote degradation of PML/RARα and restores PML expression, and increase the level of nuclear PTEN. Pretreatment of PTEN inhibitor SF1670 enhances the PI3K signaling pathway and represses NB4 cell differentiation. Moreover, the induction of PTEN attenuated the Akt phosphorylation levels, pretreatment of PI3K inhibitor LY294002 in NB4 cells, significantly augmented the cell differentiation and increased the expression of PTEN. These results therefore indicate that EGCG targets PML/RARα oncoprotein for degradation and potentiates differentiation of promyelocytic leukemia cells in combination with ATRA via PTEN.

Acute promyelocytic leukemia (APL), characterized by the presence of the promyelocytic leukemia (PML)-retinoic acid α receptor (RARα) fusion protein, responds to treatment with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). However, drug resistance and side effects restrict the application of these reagents. Hence, the development of novel therapeutic drugs for APL treatment is critical. Lapatinib, a small-molecule tyrosine kinase inhibitor, has been used in the treatment of different tumors. However, it is unclear whether lapatinib exerts antitumor effects on APL. The present study investigated the antitumor effects and potential mechanisms of lapatinib on NB4 cells derived from APL. Cell Counting Kit-8 assay and colony forming analysis indicated that lapatinib inhibited NB4 cell proliferation in a dose-dependent manner. Flow cytometry analysis revealed that lapatinib induced cell cycle arrest at the S phase and promoted cell apoptosis. Furthermore, Liu's staining and Hoechst 33258 staining revelaed that lapatinib treatment induced an apoptotic nuclear phenomenon. Furthermore, lapatinib induced apoptosis by decreasing Bcl-2 and PML-RARα levels, and by increasing the levels of Bax, cleaved PARP, cleaved caspase-3 and cleaved caspase-9. In addition, lapatinib increased the levels of phospho-p38 MAPK and phospho-JNK, and decreased the levels of phospho-Akt. The p38 inhibitor PD169316 partially blocked lapatinib-induced proliferation inhibition and apoptosis, whereas the JNK inhibitor SP600125 had no such effects. Therefore, treatment with lapatinib may be a promising strategy for APL therapy.