SOX4 reversibly induces phenotypic changes by suppressing the epithelial marker genes in human keratinocytes.

Background: SOX4 is a transcription factor belonging to the SOX (Sry-related High Mobility Group [HMG] box) family and plays a pivotal role in various biological processes at various stages of life. SOX4 is also expressed in the skin in adults and has been reported to be involved in wound healing, tumor formation, and metastasis.

Methods And Results: In this study, we investigated the role of SOX4 in keratinocyte phenotypic changes.

SNAI2 is induced by transforming growth factor-β1, but is not essential for epithelial-mesenchymal transition in human keratinocyte HaCaT cells.

Epithelial-mesenchymal transition (EMT) is a cellular process in which epithelial cells lose their epithelial traits and shift to the mesenchymal phenotype, and is associated with various biological events, such as embryogenesis, wound healing and cancer progression. The transcriptional program that promotes phenotype switching is dynamically controlled by transcription factors during EMT, including Snail (SNAI1), twist family bHLH transcription factor (TWIST) and zinc finger E-box binding homeobox 1 (ZEB1). The present study aimed to investigate the molecular mechanisms underlying EMT in squamous epithelial cells.

SMARCAD1-mediated recruitment of the DNA mismatch repair protein MutLα to MutSα on damaged chromatin induces apoptosis in human cells.

The mismatch repair (MMR) complex is composed of MutSα (MSH2-MSH6) and MutLα (MLH1-PMS2) and specifically recognizes mismatched bases during DNA replication. -Methylguanine is produced by treatment with alkylating agents, such as -methyl--nitrosourea (MNU), and during DNA replication forms a DNA mismatch ( an -methylguanine/thymine pair) and induces a G/C to A/T transition mutation. To prevent this outcome, cells carrying this DNA mismatch are eliminated by MMR-dependent apoptosis, but the underlying molecular mechanism is unclear.

Intramolecular Binding of the Rad9 C Terminus in the Checkpoint Clamp Rad9-Hus1-Rad1 Is Closely Linked with Its DNA Binding.

The human checkpoint clamp Rad9-Hus1-Rad1 (9-1-1) is loaded onto chromatin by its loader complex, Rad17-RFC, following DNA damage. The 120-amino acid (aa) stretch of the Rad9 C terminus (C-tail) is unstructured and projects from the core ring structure (CRS). Recent studies showed that 9-1-1 and CRS bind DNA independently of Rad17-RFC.

Interaction between Rad9-Hus1-Rad1 and TopBP1 activates ATR-ATRIP and promotes TopBP1 recruitment to sites of UV-damage.

The checkpoint clamp Rad9-Hus1-Rad1 (9-1-1) interacts with TopBP1 via two casein kinase 2 (CK2)-phosphorylation sites, Ser-341 and Ser-387 in Rad9. While this interaction is known to be important for the activation of ATR-Chk1 pathway, how the interaction contributes to their accumulation at sites of DNA damage remains controversial. Here, we have studied the contribution of the 9-1-1/TopBP1 interaction to the assembly and activation of checkpoint proteins at damaged DNA.

Two serine phosphorylation sites in the C-terminus of Rad9 are critical for 9-1-1 binding to TopBP1 and activation of the DNA damage checkpoint response in HeLa cells.

A heteromeric proliferating cell nuclear antigen-like ring complex 9-1-1 is comprised of Rad9, Hus1 and Rad1. When assembled, 9-1-1 binds to TopBP1 and activates the ATR-Chk1 checkpoint pathway. This binding in vitro depends on the phosphorylation of Ser-341 and Ser-387 in Rad9 and is reduced to 70% and 20% by an alanine substitution for Ser-341 (S341A) and Ser-387 (S387A), respectively, and to background level by their simultaneous substitution (2A).

Casein kinase 2-dependent phosphorylation of human Rad9 mediates the interaction between human Rad9-Hus1-Rad1 complex and TopBP1.

The checkpoint clamp Rad9-Hus1-Rad1 (9-1-1) is loaded by the Rad17-RFC complex onto chromatin after DNA damage and plays a key role in the ATR-dependent checkpoint activation. Here, we demonstrate that in vitro casein kinase 2 (CK2) specifically interacts with human 9-1-1 and phosphorylates serines 341 and 387 (Ser-341 and Ser-387) in the C-terminal tail of Rad9. Interestingly, phosphorylated Ser-387 has previously been reported to be required for interacting with a checkpoint mediator TopBP1.