Histone H3 lysine 9 methylation has been proposed to provide a major "switch" for the functional organization of chromosomal subdomains. Here, we show that the murine Suv39h histone methyltransferases (HMTases) govern H3-K9 methylation at pericentric heterochromatin and induce a specialized histone methylation pattern that differs from the broad H3-K9 methylation present at other chromosomal regions. Suv39h-deficient mice display severely impaired viability and chromosomal instabilities that are associated with an increased tumor risk and perturbed chromosome interactions during male meiosis. These in vivo data assign a crucial role for pericentric H3-K9 methylation in protecting genome stability, and define the Suv39h HMTases as important epigenetic regulators for mammalian development.

Multipotent, self-renewing neural stem cells reside in the embryonic mouse telencephalic germinal zone. Using an in vitro neurosphere assay for neural stem cell proliferation, we demonstrate that FGF-responsive neural stem cells are present as early as E8.5 in the anterior neural plate, but EGF-responsive neural stem cells emerge later in development in a temporally and spatially specific manner. By separately blocking EGF and FGF2 signaling, we also show that EGF alone and FGF2 alone can independently elicit neural stem cell proliferation and at relatively high cell densities separate cell nonautonomous effects can substantially enhance the mitogen-induced proliferation. At lower cell densities, neural stem cell proliferation is additive in the presence of EGF and FGF2 combined, revealing two different stem cell populations. However, both FGF-responsive and EGF-responsive neural stem cells retain their self-renewal and multilineage potential, regardless of growth factor conditions. These results support a model in which separate, lineage-related EGF- and FGF-responsive neural stem cells are present in the embryonic telencephalic germinal zone.

c-Jun is a major component of the heterodimeric transcription factor AP-1 and is essential for embryonic development, as fetuses lacking Jun die at mid-gestation with impaired hepatogenesis and primary Jun-/- fibroblasts have a severe proliferation defect and undergo premature senescence in vitro. c-Jun and AP-1 activities are regulated by c-Jun N-terminal phosphorylation (JNP) at serines 63 and 73 through Jun N-terminal kinases(JNKs). JNP is thought to be required for the anti-apoptotic function of c-Jun during hepatogenesis, as mice lacking the JNK kinase SEK1 exhibit liver defects similar to those seen in Jun-/- fetuses. To investigate the physiological relevance of JNP, we replaced endogenous Jun by a mutant Jun allele with serines 63 and 73 mutated to alanines (Jun(tm1wag); hereafter referred to as JunAA). Here we show that primary JunAA fibroblasts have proliferation- and stress-induced apoptotic defects, accompanied by reduced AP-1 activity. JunAA mice are viable and fertile, smaller than controls and resistant to epileptic seizures and neuronal apoptosis induced by the excitatory amino acid kainate. Primary mutant neurons are also protected from apoptosis and exhibit unaltered JNK activity. Our results provide evidence that JNP is dispensable for mouse development, and identify c-Jun as the essential substrate of JNK signalling during kainate-induced neuronal apoptosis.

Mice and cells lacking the epidermal growth factor receptor (EGFR) were generated to examine its physiological role in vivo. Mutant fetuses are retarded in growth and die at mid-gestation in a 129/Sv genetic background, whereas in a 129/Sv x C57BL/6 cross some survive until birth and even to postnatal day 20 in a 129/Sv x C57BL/6 x MF1 background. Death in utero probably results from a defect in the spongiotrophoblast layer of the placenta. Newborn mutant mice have open eyes, rudimentary whiskers, immature lungs, and defects in the epidermis, correlating with the expression pattern of the EGFR as monitored by beta-galactosidase activity. These defects are probably cell-autonomous because chimeric mice generated with EGFR-/- embryonic stem cells contribute small amounts of mutant cells to some organs. These results indicate that the EGFR regulates epithelial proliferation and differentiation and that the genetic background influences the resulting phenotype.

SUMMARY Initiation of pancreatic ductal adenocarcinoma (PDA) is definitively linked to activating mutations in the KRAS oncogene. However, PDA mouse models show that mutant Kras expression early in development gives rise to a normal pancreas, with tumors forming only after a long latency or pancreatitis induction. Here we show that oncogenic KRAS upregulates endogenous EGFR expression and activation, the latter being dependent upon the EGFR ligand sheddase, ADAM17. Genetic ablation or pharmacological inhibition of EGFR or ADAM17 effectively eliminates KRAS-driven tumorigenesis in vivo. Without EGFR activity, active RAS levels are not sufficient to induce robust MEK/ERK activity, a requirement for epithelial transformation.

Clinical evidence indicates that mutation/activation of EGF receptors (EGFRs) is mutually exclusive with the presence of K-RAS oncogenes in lung and colon tumors. We have validated these observations using genetically engineered mouse models. However, development of pancreatic ductal adenocarcinomas driven by K-Ras oncogenes are totally dependent on EGFR signaling. Similar results were obtained using human pancreatic tumor cell lines. EGFRs were also essential even in the context of pancreatic injury and absence of p16Ink4a/p19Arf. Only loss of p53 made pancreatic tumors independent of EGFR signaling. Additional inhibition of PI3K and STAT3 effectively prevented proliferation of explants derived from these p53-defective pancreatic tumors. These findings may provide the bases for more rational approaches to treat pancreatic tumors in the clinic.

Summary Epidermal growth factor receptor (EGFR) is known to be critically involved in tissue development and homeostasis as well as in the pathogenesis of cancer. Here we showed that Foxp3+ regulatory T (Treg) cells express EGFR under inflammatory conditions. Stimulation with the EGF-like growth factor Amphiregulin (AREG) markedly enhanced Treg cell function in vitro, and in a colitis and tumor vaccination model we showed that AREG was critical for efficient Treg cell function in vivo. In addition, mast cell-derived AREG fully restored optimal Treg cell function. These findings reveal EGFR as a component in the regulation of local immune responses and establish a link between mast cells and Treg cells. Targeting of this immune regulatory mechanism may contribute to the therapeutic successes of EGFR-targeting treatments in cancer patients.

It is established that tumor cell-derived VEGF acts on endothelial cells to promote angiogenesis and tumor growth. Here, we demonstrate that in K5-SOS-dependent mouse skin tumors, autocrine VEGF is required for tumor cell proliferation in a cell-autonomous and angiogenesis-independent manner. VEGF is upregulated in SOS-expressing tumors, and its deletion in epidermal cells delays tumorigenesis by suppressing angiogenesis and tumor cell proliferation. Epidermis-specific Flt1 deletion also impairs tumorigenesis and proliferation. Surprisingly, complete tumor inhibition occurs in the absence of VEGF in EGFR mutant mice, demonstrating that VEGFR and EGFR synergize in neoplastic cells to promote tumor growth. Mechanistically, K5-SOS upregulates VEGF, Flt1, and Neuropilin-1 in an Erk-dependent manner, thereby activating an autocrine proliferation loop, whereas EGFR prevents tumor cells from apoptosis. Moreover, Flt1 is upregulated in human SCC, and its inhibition in SCC cells impairs proliferation. Thus, in addition to regulating angiogenesis, VEGF has to be considered as a potent growth factor for epidermal tumors.