Protein Phosphatase 2A-Dependent Mitotic hnRNPA1 Dephosphorylation and TERRA Formation Facilitate Telomere Capping.

The heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), telomeric repeat-containing RNA (TERRA), and protection of telomeres 1 (POT1) have been reported to orchestrate to displace replication protein A (RPA) from telomeric overhangs, ensuring orderly telomere replication and capping. Our previous studies further demonstrated that DNA-dependent protein kinase catalytic subunit (DNA-PKcs)-dependent hnRNPA1 phosphorylation plays a crucial role in the promotion of hnRNPA1 binding to telomeric overhangs and RPA displacement during G2-M phases. However, it is unclear that how the subsequent exchange between hnRNPA1 and POT1 is orchestrated. Here we report that the protein phosphatase 2A (PP2A) depends on its scaffold subunit, which is called PPP2R1A, to interact with and dephosphorylate hnRNPA1 in the late M phase. Furthermore, PP2A-mediated hnRNPA1 dephosphorylation and TERRA accumulation act in concert to promote the hnRNPA1-to-POT1 switch on telomeric single-stranded DNA. Consequently, defective PPP2R1A results in ataxia telangiectasia and Rad3-related (ATR)-mediated DNA damage response at telomeres as well as induction of fragile telomeres. Combined inhibition of ATR and PP2A induces entry into a catastrophic mitosis and leads to synthetic lethality of tumor cells. In addition, PPP2R1A levels correlate with clinical stages and prognosis of multiple types of cancers. Taken together, our results indicate that PP2A is critical for telomere maintenance. IMPLICATIONS: This study demonstrates that the PP2A-dependent hnRNPA1 dephosphorylation and TERRA accumulation facilitates the formation of the protective capping structure of newly replicated telomeres, thus exerting essential oncogenic role in tumorigenesis.

[Histiocytic sarcoma:a clinicopathologic study of 4 cases].

OBJECTIVE: To investigate the clinicopathologic features, immunophenotyping, differential diagnoses and prognosis of histiocytic sarcoma (HS). METHODS: The clinical and pathologic findings of 4 cases of HS were reviewed. The samples were used for paraffin section, HE stain, immunohistochemistry stain by EnVision method, electron microscope observation. Follow-up information was available in all patients. RESULTS: The age of patients, 2 males and 2 females, ranged from 22 to 65 years old (median, 43.25 years). The sites of involvement included lymph node (2 cases), skin or soft tissue (1 case) and colon (1 case). The tumor cells were widespread infiltration, diffused distribution, no adhesion to each other. Tumor cells were middling and large, round, orbicular-ovate, polygon, epithelium appearance, plentiful cytoplasm and acidophilia, cystose. Nucelus was round, orbicular-ovate, dissymmetry. Nuclear chromatin was vacuole appearance, basophilia nucleolus, caryocinesia and pathological mitotic figure. Three of the cases showed conjugate nuclei, increased pleomorphism with multinucleated tumor giant cell formation. Focal cytoplasmic with foamy appearance was identified in 2 cases. One case demonstrated foci of spindly sarcomatoid appearance. Hemophagocytosis was identified in 2 cases. The tumor cells of 4 cases were often accompanied by various numbers of inflammatory cells. Immunohistochemical study showed that all cases were diffusely positive for α-1-ACT, CD68, CDl63 and lysozyme. Three of 4 cases also expressed CD45, CD45RO. The electron microscope results of 4 cases showed that the tumor cells were plentiful cytoplasm and a few cytolysosome in the cytoplasm, and no birbeck cytorrhyctes, cell-cell junction and digitation. Amongst the 4 patients with follow-up information available, three died of the disease 6-13 months after diagnosis. One patient, whose lesion was localized at the skin and soft tissue, survived at the present time. CONCLUSION: HS was a scarce malignant tumor with mature histiocyte morphology and immunophenotype character. The diagnosis should be based on tissue morphology, immunohistochemistry and electron microscope observation to exclude other disorders.

[Alteration of ERalpha expression and tumor invasion by RNA interference against metastasis associated-1 gene in human breast cancer cells].

OBJECTIVE: To investigate the inhibitory effect on MTA1 gene by MTA1 short hairpin RNA (shRNA), downstream regulation of expression of ERa and invasion of human breast cancer cells. METHODS: Recombinant plasmid pGenesil-1/MTA1 was constructed and transfected into human breast cancer cell lines MDA-MB-231 and MCF-7. Fluorescence microscopy was used to evaluate the efficacy of transfection. The transcription expression of MTA1 and MMP-9 gene were determined by reverse transcription-polymerase chain reaction (RT-PCR), the protein expression of ERalpha and MMP-9 were determined by immunohistochemical and western blot. The invasion ability was evaluated by Boyden chamber invasive assay. RESULTS: Recombinant plasmid pGenesil-1/MTA1 was constructed and transfected into MDA-MB-231 (82.5%) and MCF-7 (78.2%) successfully. After the transfection, MTA1 mRNA was suppressed in both cell lines (80.2% and 58.7%). The expression of ERalpha protein became positive in transfected MDA-MB-231 cell, and the expression of MMP-9 mRNA were down-regulated. The invasion ability was decreased (27.2% +/- 2.1)% compared with (76.3% +/- 2.4%), (P < 0.05). In contrast, transfected MCF-7 cells failed to show significant difference in the expression of ERalpha and MMP-9, without change of the invasion ability (P > 0.05). CONCLUSIONS: RNA interference can effectively suppress the expression of MTA1 in human breast cancer cells. An induction of ERalpha protein and suppression of MMP-9 may be related to the decrease of tumor cell invasive ability. RNA interference involving MTA1 gene may provide an effective anti-cancer gene therapy.