Background:The regulation of multi-functional DYNLL1 is poorly understood. Results: ASCIZ activates Dynll1 gene expression and is inhibited by DYNLL1 binding to its transcription activation domain. Conclusion: ASCIZ plays a key role in the auto-regulation of DYNLL1 levels. Significance: This is the first case where a gene product directly inhibits its main transcriptional activator while bound at its own promoter.

Dicer is a key player in microRNA (miRNA) and RNA interference (RNAi) pathways, processing miRNA precursors and doublestranded RNA into ∼21-nt-long products ultimately triggering sequence-dependent gene silencing. Although processing of substrates in vertebrate cells occurs in the cytoplasm, there is growing evidence suggesting Dicer is also present and functional in the nucleus. To address this possibility, we searched for a nuclear localization signal (NLS) in human Dicer and identified its C-terminal double-stranded RNA binding domain (dsRBD) as harboring NLS activity. We show that the dsRBD-NLS can mediate nuclear import of a reporter protein via interaction with importins β, 7, and 8. In the context of full-length Dicer, the dsRBD-NLS is masked. However, duplication of the dsRBD localizes the full-length protein to the nucleus. Furthermore, deletion of the N-terminal helicase domain results in partial accumulation of Dicer in the nucleus upon leptomycin B treatment, indicating that CRM1 contributes to nuclear export of Dicer. Finally, we demonstrate that human Dicer has the ability to shuttle between the nucleus and the cytoplasm. We conclude that Dicer is a shuttling protein whose steady-state localization is cytoplasmic.

B cell development requires the Zinc-finger protein and ATM substrate ASCIZ to signal through DYNLL1 and Bim.

Zn2+-finger proteins comprise one of the largest protein superfamilies with diverse biological functions. The ATM substrate Chk2-interacting Zn2+-finger protein (ASCIZ; also known as ATMIN and ZNF822) was originally linked to functions in the DNA base damage response and has also been proposed to be an essential cofactor of the ATM kinase. Here we show that absence of ASCIZ leads to p53-independent late-embryonic lethality in mice. Asciz-deficient primary fibroblasts exhibit increased sensitivity to DNA base damaging agents MMS and H2O2, but Asciz deletion or knock-down does not affect ATM levels and activation in mouse, chicken, or human cells. Unexpectedly, Asciz-deficient embryos also exhibit severe respiratory tract defects with complete pulmonary agenesis and severe tracheal atresia. Nkx2.1-expressing respiratory precursors are still specified in the absence of ASCIZ, but fail to segregate properly within the ventral foregut, and as a consequence lung buds never form and separation of the trachea from the oesophagus stalls early. Comparison of phenotypes suggests that ASCIZ functions between Wnt2-2b/ß-catenin and FGF10/FGF-receptor 2b signaling pathways in the mesodermal/endodermal crosstalk regulating early respiratory development. We also find that ASCIZ can activate expression of reporter genes via its SQ/TQ-cluster domain in vitro, suggesting that it may exert its developmental functions as a transcription factor. Altogether, the data indicate that, in addition to its role in the DNA base damage response, ASCIZ has separate developmental functions as an essential regulator of respiratory organogenesis.

PAX5 is a tumor suppressor in B-ALL, while the role of PAX5 fusion proteins in B-ALL development is largely unknown. Here, we studied the function of PAX5-ETV6 and PAX5-FOXP1 in mice expressing these proteins from the Pax5 locus. Both proteins arrested Blymphopoiesis at the pro-B to pre-B-cell transition and, contrary to their proposed dominant-negative role, did not interfere with the expression of most regulated Pax5 target genes. Pax5-Etv6, but not Pax5-Foxp1, cooperated with loss of the Cdkna2a/b tumor suppressors in promoting B-ALL development. Regulated Pax5-Etv6 target genes identified in these B-ALLs encode proteins implicated in pre-B-cell receptor (BCR) signaling and migration/adhesion, which could contribute to the proliferation, survival, and tissue infiltration of leukemic B cells. Together with similar observations made in human PAX5-ETV6 + B-ALLs, these data identified PAX5-ETV6 as a potent oncoprotein that drives B-cell leukemia development.

How MYC promotes the development of cancer remains to be fully understood. Here, we report that the Zn(2+)-finger transcription factor ASCIZ (ATMIN, ZNF822) synergizes with MYC to activate the expression of dynein light chain (DYNLL1, LC8) in the murine Eμ-Myc model of lymphoma. Deletion of Asciz or Dynll1 prevented the abnormal expansion of pre-B cells in pre-cancerous Eμ-Myc mice and potentiated the pro-apoptotic activity of MYC in pre-leukemic immature B cells. Constitutive loss of Asciz or Dynll1 delayed lymphoma development in Eμ-Myc mice, and induced deletion of Asciz in established lymphomas extended the survival of tumor-bearing mice. We propose that ASCIZ-dependent upregulation of DYNLL1 levels is essential for the development and expansion of MYC-driven lymphomas by enabling the survival of pre-neoplastic and malignant cells.

While PAX5 is an important tumor suppressor gene in B‐cell acute lymphoblastic leukemia (B‐ALL), it is also involved in oncogenic translocations coding for diverse PAX5 fusion proteins. PAX5‐JAK2 encodes a protein consisting of the PAX5 DNA‐binding region fused to the constitutively active JAK2 kinase domain. Here, we studied the oncogenic function of the PAX5‐JAK2 fusion protein in a mouse model expressing it from the endogenous Pax5 locus, resulting in inactivation of one of the two Pax5 alleles. Pax5Jak2/+ mice rapidly developed an aggressive B‐ALL in the absence of another cooperating exogenous gene mutation. The DNA‐binding function and kinase activity of Pax5‐Jak2 as well as IL‐7 signaling contributed to leukemia development. Interestingly, all Pax5Jak2/+ tumors lost the remaining wild‐type Pax5 allele, allowing efficient DNA‐binding of Pax5‐Jak2. While we could not find evidence for a nuclear role of Pax5‐Jak2 as an epigenetic regulator, high levels of active phosphorylated STAT5 and increased expression of STAT5 target genes were seen in Pax5Jak2/+ B‐ALL tumors, implying that nuclear Pax5‐Jak2 phosphorylates STAT5. Together, these data reveal Pax5‐Jak2 as an important nuclear driver of leukemogenesis by maintaining phosphorylated STAT5 levels in the nucleus.

The ATM substrate Chk2-interacting Zn 2+ -finger protein (ASCIZ, also known as ATMIN and ZNF822) has previously been reported to be important for the repair of methylating and oxidative DNA damage, and it has also been proposed to regulate the stability and DNA damage-independent activation of the ATM kinase. While the role of the protein in the regulation of ATM remains controversial, two recent ASCIZ mouse knockout papers confirm its role in the DNA base damage response, including oxidative stress resistance in vivo. Similar to other DNA base damage repair proteins, ASCIZ is essential for embryonic development, with lethality of Asciz-null embryos around day E16.5 post conception. Unexpectedly, absence of ASCIZ also leads to severe organ development defects, most notably, complete absence of lungs similar to mutants in Wnt2-2b/b-catenin and FGF10/ FGFR2b signaling pathways. Together with evidence that ASCIZ can activate transcription in vitro, the phenotype indicates that ASCIZ has dual functions as an efficiency factor for DNA base damage repair as well as a key transcriptional regulator of early lung development.