In mammalian cells, a specific stress‐activated protein kinase (SAPK/JNK) pathway is activated in response to inflammatory cytokines, injury from heat, chemotherapeutic drugs and UV or ionizing radiation. The mechanisms that link these stimuli to activation of the SAPK/JNK pathway in different tissues remain to be identified. We have developed and applied a PCR‐based subtraction strategy to identify novel genes that are differentially expressed at specific developmental points in hematopoiesis. We show that one such gene, hematopoietic progenitor kinase 1 (hpk1), encodes a serine/threonine kinase sharing similarity with the kinase domain of Ste20. HPK1 specifically activates the SAPK/JNK pathway after transfection into COS1 cells, but does not stimulate the p38/RK or mitogen‐activated ERK signaling pathways. Activation of SAPK requires a functional HPK1 kinase domain and HPK1 signals via the SH3‐containing mixed lineage kinase MLK‐3 and the known SAPK activator SEK1. HPK1 therefore provides an example of a cell type‐specific input into the SAPK/JNK pathway. The developmental specificity of its expression suggests a potential role in hematopoietic lineage decisions and growth regulation.

Mixed lineage kinase‐3 (MLK‐3) is a 97 kDa serine/threonine kinase with multiple interaction domains, including a Cdc42 binding motif, but unknown function. Cdc42 and the related small GTP binding protein Rac1 can activate the SAPK/JNK and p38/RK stress‐responsive kinase cascades, suggesting that MLK‐3 may have a role in upstream regulation of these pathways. In support of this role, we demonstrate that MLK‐3 can specifically activate the SAPK/JNK and p38/RK pathways, but has no effect on the activation of ERKs. Immunoprecipitated MLK‐3 catalyzed the phosphorylation of SEK1 in vitro, and co‐transfected MLK‐3 induced phosphorylation of SEK1 and MKK3 at sites required for activation, suggesting direct regulation of these protein kinases. Furthermore, interactions between MLK‐3 and SEK and MLK‐3 and MKK6 were observed in co‐precipitation experiments. Finally, kinase‐dead mutants of MLK‐3 blocked activation of the SAPK pathway by a newly identified mammalian analog of Ste20, germinal center kinase, but not by MEKK, suggesting that MLK‐3 functions to activate the SAPK/JNK and p38/RK cascades in response to stimuli transduced by Ste20‐like kinases.

Approximately 8-12% of melanoma is inherited in an autosomal dominant fashion with variable penetrance. A chromosome 9p21 locus has been linked to this disease in 50-80% of affected families. CDKN2A (also known as P16, INK4, p16INK4A and MTS1) is allelic to this locus and encodes a cdk4/cdk6 kinase inhibitor that constrains cells from progressing through the G1 restriction point. Although germline CDKN2A coding mutations cosegregate with melanoma in 25-60% of families predisposed to the disease, there remains a number of mutation-negative families that demonstrate linkage of inherited melanoma to 9p21 markers. We show here that a subset of these kindreds possess a G-->T transversion at base -34 of CDKN2A, designated G-34T. This mutation gives rise to a novel AUG translation initiation codon that decreases translation from the wild-type AUG. The G-34T mutation is not seen in controls, segregates with melanoma in families and, on the basis of haplotyping studies, probably arose from a common founder in the United Kingdom. Characterization of this and other CDKN2A non-coding mutations should have an impact on current efforts to identify susceptible melanoma-prone families and individuals.

BACKGROUND Hereditary pancreatic carcinoma shows extant phenotypic and genotypic heterogeneity as evidenced by its integral association with a variety of hereditary cancer syndromes inclusive of the familial atypical multiple mole melanoma (FAMMM) syndrome in concert with CDKN2A (p16) germline mutations. METHODS Creighton University's familial pancreatic carcinoma resource comprises 159 families of which 19 (12%) show the FAMMM cutaneous phenotypes. The authors describe eight families with the FAMMM–pancreatic carcinoma (FAMMM‐PC) association in concert with a CDKN2A germline mutation. Each family was thoroughly educated about all facets of the study, including the molecular genetics, reduced penetrance of CDKN2A mutations, and their variable expressivity. Genetic counseling was provided to each patient. RESULTS Diversity in cancer presentation within and among the families was noteworthy, wherein melanoma predominated in certain of the families whereas pancreatic carcinoma predominated in others. Early‐onset pancreatic carcinoma (at ages 35, 45, 46, and 49 years) appeared in some of the families whereas markedly later‐onset pancreatic carcinoma occurred in others. There were four incidences of melanoma and pancreatic carcinoma as double primaries in the same individuals. One patient with melanoma and pancreatic carcinoma had a third primary of breast carcinoma. Another patient had sarcoma, esophageal carcinoma, and two melanoma primaries, whereas his daughter had sarcoma and was a carrier of a CDKN2A mutation. CONCLUSIONS The authors suggest that these tumors may collectively, in concert with CDKN2A mutations, constitute a “new” putative hereditary carcinoma syndrome referred to as FAMMM‐PC. More clinical and molecular genetic research on additional families with pancreatic carcinoma in concert with the FAMMM will be required. Cancer 2002;94:84–96. © 2002 American Cancer Society.

Some patients with multiple primary melanomas but without family histories of the disease have germ-line mutations of the CDKN2A gene. The presence of multiple primary melanomas may signal a genetic susceptibility to melanoma not only in the index patient but also in family members, who may benefit from melanoma-surveillance programs.