The IL-6/JAK/Stat3 feed-forward loop drives tumorigenesis and metastasis.

We have investigated the importance of interleukin-6 (IL-6) in promoting tumor growth and metastasis. In human primary breast cancers, increased levels of IL-6 were found at the tumor leading edge and positively correlated with advanced stage, suggesting a mechanistic link between tumor cell production of IL-6 and invasion. In support of this hypothesis, we showed that the IL-6/Janus kinase (JAK)/signal transducer and activator of transcription 3 (Stat3) pathway drives tumor progression through the stroma and metastatic niche. Overexpression of IL-6 in tumor cell lines promoted myeloid cell recruitment, angiogenesis, and induced metastases. We demonstrated the therapeutic potential of interrupting this pathway with IL-6 receptor blockade or by inhibiting its downstream effectors JAK1/2 or Stat3. These clinically relevant interventions did not inhibit tumor cell proliferation in vitro but had profound effects in vivo on tumor progression, interfering broadly with tumor-supportive stromal functions, including angiogenesis, fibroblast infiltration, and myeloid suppressor cell recruitment in both the tumor and pre-metastatic niche. This study provides the first evidence for IL-6 expression at the leading edge of invasive human breast tumors and demonstrates mechanistically that IL-6/JAK/Stat3 signaling plays a critical and pharmacologically targetable role in orchestrating the composition of the tumor microenvironment that promotes growth, invasion, and metastasis.

Cyclin-dependent kinase 9 (Cdk9) of fission yeast is activated by the CDK-activating kinase Csk1, overlaps functionally with the TFIIH-associated kinase Mcs6, and associates with the mRNA cap methyltransferase Pcm1 in vivo.

Cyclin-dependent kinase 9 (Cdk9) of fission yeast is an essential ortholog of metazoan positive transcription elongation factor b (P-TEFb), which is proposed to coordinate capping and elongation of RNA polymerase II (Pol II) transcripts. Here we show that Cdk9 is activated to phosphorylate Pol II and the elongation factor Spt5 by Csk1, one of two fission yeast CDK-activating kinases (CAKs). Activation depends on Cdk9 T-loop residue Thr-212. The other CAK-Mcs6, the kinase component of transcription factor IIH (TFIIH)-cannot activate Cdk9. Consistent with the specificities of the two CAKs in vitro, the kinase activity of Cdk9 is reduced approximately 10-fold by csk1 deletion, and Cdk9 complexes from csk1Delta but not csk1+ cells can be activated by Csk1 in vitro. A cdk9(T212A) mutant is viable but phenocopies conditional growth defects of csk1Delta strains, indicating a role for Csk1-dependent activation of Cdk9 in vivo. A cdk9(T212A) mcs6(S165A) strain, in which neither Cdk9 nor Mcs6 can be activated by CAK, has a synthetic growth defect, implying functional overlap between the two CDKs, which have distinct but overlapping substrate specificities. Cdk9 forms complexes in vivo with the essential cyclin Pch1 and with Pcm1, the mRNA cap methyltransferase. The carboxyl-terminal region of Cdk9, through which it interacts with another capping enzyme, the RNA triphosphatase Pct1, is essential. Together, the data support a proposed model whereby Cdk9/Pch1-the third essential CDK-cyclin complex described in fission yeast-helps to target the capping apparatus to the transcriptional elongation complex.

Genomic Alterations in Gastrointestinal Stromal Tumors as Revealed by Conventional and Array-based Comparative Genomic Hybridization.

Gastrointestinal stromal tumor (GIST) is the most commonly occurring mesenchymal neoplasm of the gastrointestinal tract, accounting for 80 percent of these tumors. GIST is highly unresponsive to standard chemotherapy, particularly in patients with advanced or metastatic disease. Recent molecular studies have shown that activating c-kit (KIT) mutations are detectable in a large proportion (>75%) of tumors, between 78% (1) and 89% (2). Approximately 30% of tumors without an identifiable KIT mutation exhibit PDGFRA mutations (3). Furthermore, the KIT mutations are heterogeneous, some being known to confer a relatively better prognosis than others (1). Gross cytogenetic abnormalities associated with GIST appear to be similar regardless of whether a KIT mutation is identified. The molecular genetic alterations associated with multistep GIST tumorigenesis, particularly those which confer intrinsic or acquired resistance to both standard as well as targeted therapeutic approaches, however, are not fully recognized. As an initial approach to identify chromosomal sites of candidate gene(s), which may predict overall clinical and biologic behavior of GISTs, as they relate to response to the specific therapeutic drug Gleevec, we analyzed six GIST samples using both conventional as well as array-based Comparative Genomic Hybridization (CGH). The common abnormalities detected by CGH in low and high grade tumors included loss of all or part of chromosome 14; an entire chromosome 14 was lost in four tumor samples, with the remaining two samples exhibiting loss of the 14q22-q32.3 region. Other recurrent abnormalities included loss of the 1p chromosomal region (four tumor samples), loss of part or entire chromosome 9 (only in metastatic tumors), loss of chromosomes 15 and 22, and a gain of the chromosome 3q region in three samples each. Array- based CGH performed using human BAC arrays (1400V11 Spectral Genomics Chip™) on the other hand, not only detected recurrent abnormalities of the chromosomes and chromosomal sites mentioned above, but also identified losses of additional chromosomal sites on chromosomes 6q and 13q. Array-based CGH further delineated the regions of loss or gain to specific chromosome bands or sub bands based on location of chromosomal site-specific BACs. The specific regions of losses are located at 1p36.2-36.3,6q12,9p13-ter,13q33.33-q34, and gain or amplification of chromosomal DNA at bands 3q26-27. It is interesting to note that some of the chromosomal sites of losses and gains also harbor gene(s) such as AFAR, RIZ1, p73(1p35-36), Akt-1(14q32), p14 and p16(9p21), NF2(22q12), ZASCI, p63 and PIK3CA oncogenes (3q26-27), all of which are known to play a major role in solid tumor pathogenesis. The role of these genes in GIST, however, remains to be seen. Thus, the results of our current study demonstrate that such a combined approach to detect global genomic alterations in GIST is significant in providing information related to chromosomal sites of potential tumor suppressor genes associated with multistep tumorigenesis; some of which also may be predictive of prognosis and clinical outcome following specific targeted therapy, which is the focus of future studies.