Jnk2 Effects on Tumor Development, Genetic Instability and Replicative Stress in an Oncogene-Driven Mouse Mammary Tumor Model

Abstract

Oncogenes induce cell proliferation leading to replicative stress, DNA damage and genomic instability. A wide variety of cellular stresses activate c-Jun N-terminal kinase (JNK) proteins, but few studies have directly addressed the roles of JNK isoforms in tumor development. Herein, we show that jnk2 knockout mice expressing the Polyoma Middle T Antigen transgene developed mammary tumors earlier and experienced higher tumor multiplicity compared to jnk2 wildtype mice. Lack of jnk2 expression was associated with higher tumor aneuploidy and reduced DNA damage response, as marked by fewer pH2AX and 53BP1 nuclear foci. Comparative genomic hybridization further confirmed increased genomic instability in PyV MT/jnk2−/− tumors. In vitro, PyV MT/jnk2−/− cells underwent replicative stress and cell death as evidenced by lower BrdU incorporation, and sustained chromatin licensing and DNA replication factor 1 (CDT1) and p21Waf1 protein expression, and phosphorylation of Chk1 after serum stimulation, but this response was not associated with phosphorylation of p53 Ser15. Adenoviral overexpression of CDT1 led to similar differences between jnk2 wildtype and knockout cells. In normal mammary cells undergoing UV induced single stranded DNA breaks, JNK2 localized to RPA (Replication Protein A) coated strands indicating that JNK2 responds early to single stranded DNA damage and is critical for subsequent recruitment of DNA repair proteins. Together, these data support that JNK2 prevents replicative stress by coordinating cell cycle progression and DNA damage repair mechanisms.

APRIL Binding to BCMA Activates a JNK2–FOXO3–GADD45 Pathway and Induces a G2/M Cell Growth Arrest in Liver Cells

“…In a very elegant study, Sabapathy et al (48) showed that JNK1 was proproliferative via c-Jun phosphorylation, whereas JNK2 was antiproliferative through negative regulation of c-jun expression/phosphorylation and ubiquitin binding to c-jun. Furthermore, in a tissue type-and cell typespecific manner, JNK2 has an important role in regulating several molecules related to cell cycle progression checkpoints, especially under DNA damage conditions, leading to cell cycle arrest (69)(70)(71)(72). Hepatocytes from Jnk2 2/2 mice, however, exhibit increased proliferation rates compared with their wild-type counterparts (73), a finding in line with our results in HCC cells.…”

An In Vivo Functional Screen Identifies JNK Signaling As a Modulator of Chemotherapeutic Response in Breast Cancer

“…However, paradoxically, studies have demonstrated both a protumorigenic (16,41,42) and a tumor- (43,44) role for the JNK family, with duration of activation and context both implicated in defining the response (45). A major consideration in addressing these contrasting results is that reports of JNK acting as a tumor suppressor have studied the formation of primary tumors (46)(47)(48), where JNKmediated activation of apoptosis has an inhibitory role. In contrast, the in vivo screen described here represents an advanced tumor setting and our functional analyses confirm the complex interplay of prosurvival and proapoptotic signaling via JNK, which has important implications for the use of JNK inhibitors as potential therapeutics in cancer (12).…”

The 2 Faces of JNK Signaling in Cancer

“…42 Increased p53 protein stability upon phosphorylation by JNK may be one important mechanism by which JNK signaling contributes to mediating oncogene-induced senescence and cell cycle arrest as a means to maintain genomic stability and to suppress tumorigenesis. 37,41 However, unlike jnk1 −/− mice, jnk2 −/− mice and mice harboring a specific deletion of mkk4 in keratinocytes were resistant to the 2-stage chemical carcinogenesis protocol. 43,44 Similarly, mice lacking JNK1 exhibited a marked decrease in gastric carcinogenesis induced by N-methyl-N-nitrosourea compared to their wild-type counterparts.…”