The role of JAK/STAT signalling in the pathogenesis, prognosis and treatment of solid tumours.

Aberrant activation of intracellular signalling pathways confers malignant properties on cancer cells. Targeting intracellular signalling pathways has been a productive strategy for drug development, with several drugs acting on signalling pathways already in use and more continually being developed. The JAK/STAT signalling pathway provides an example of this paradigm in haematological malignancies, with the identification of JAK2 mutations in myeloproliferative neoplasms leading to the development of specific clinically effective JAK2 inhibitors, such as ruxolitinib. It is now clear that many solid tumours also show activation of JAK/STAT signalling. In this review, we focus on the role of JAK/STAT signalling in solid tumours, examining the molecular mechanisms that cause inappropriate pathway activation and their cellular consequences. We also discuss the degree to which activated JAK/STAT signalling contributes to oncogenesis. Studies showing the effect of activation of JAK/STAT signalling upon prognosis in several tumour types are summarised. Finally, we discuss the prospects for treating solid tumours using strategies targeting JAK/STAT signalling, including what can be learned from haematological malignancies and the extent to which results in solid tumours might be expected to differ.

MsSOCS expression indicates a potential role for JAK/STAT signalling in the early stages of Manduca sexta spermatogenesis.

Our understanding of the Drosophila melanogaster testis stem cell niche has identified the signalling pathways required to maintain stem cells and promote self-renewal. Here we present the first detailed examination of the testes stem cell niche in the lepidopteran Manduca sexta . We show that larval testes contain hub-like structures surrounded by mitotically active cells likely to represent a self-renewing stem cell population. In addition, we have cloned DNA fragments encoding parts of M. sexta Signal Transducer and Activators of Transcription (STAT) and Suppressor of Cytokine Signalling (SOCS) homologues and show that expression of MsSOCS is upregulated in hub-adjacent cells. Given the conservation of socs-like genes and their regulation as Janus Kinases/Signal Transducer and Activators Transcription (JAK/STAT) pathway targets, we suggest that increased expression within the testis stem cells indicates increased levels of JAK/STAT signalling and a conserved role for pathway signalling in testis stem cell maintenance.

Multiple roles for four-jointed in planar polarity and limb patterning.

Insect cuticles have been a model system for the study of planar polarity for many years and a number of genes required for this process have been identified. These genes organise the polarised arrangement of hairs on the legs, wings, thorax, and abdomen of adult Drosophila. It has previously been shown that four-jointed is involved in planar polarity decisions in the eye as well as proximal distal leg and wing development. We now present evidence that four-jointed is expressed in a gradient through the developing wing and show that it is required for planar polarity determination in both the wing and the abdomen. Clones of cells either lacking or ectopically expressing four-jointed cause both autonomous and nonautonomous repolarisation of hairs in these tissues. We propose that the inferred four-jointed expression gradient is important for planar polarity establishment and that local inversions of the gradient by the clones are the probable cause of the observed polarity phenotypes. In addition we observe defects in wing vein development. The subtle phenotypes of mutant flies, and the diverse patterning processes in which it is involved, suggest that four-jointed may act as a modifier of the activity of multiple other signalling factors.

Sex determination: co-opted signals determine gender.

The Drosophila JAK-STAT pathway and its ligand Unpaired are required for a wide range of developmental processes. Recent results have identified Unpaired as an activator of sex-lethal and revealed a new role for the JAK-STAT pathway in sex determination.

The roles of the Drosophila JAK/STAT pathway.

The JAK/STAT signal transduction pathway has been conserved throughout evolution such that true structural and functional homologues of components originally identified in vertebrate systems are also present in the model genetic system Drosophila melanogaster. In addition to roles during larval hematopoiesis reminiscent of the requirement for this pathway in mammalian systems, the JAK/STAT pathway in Drosophila is also involved in a number of other developmental events. Recent data has demonstrated further roles for the JAK/STAT pathway in the establishment of sexual identity via the early embryonic expression of Sex lethal, the segmentation of the embryo via the control of pair rule genes including even skipped and the establishment of polarity within the adult compound eye via a mechanism that includes the four jointed gene. Use of the powerful genetics in the model organism Drosophila may identify new components of the JAK/STAT pathway, define new roles for this pathway, and provide insights into the function of this signal transduction system. Here we review the roles of STAT and its associated signaling pathway during both embryonic and adult stages of Drosophila development and discuss future prospects for the identification and characterization of novel pathway components and targets. Oncogene (2000).

The four-jointed gene is required in the Drosophila eye for ommatidial polarity specification.

BACKGROUND: The Drosophila eye is composed of about 800 ommatidia, each of which becomes dorsoventrally polarised in a process requiring signalling through the Notch, JAK/STAT and Wingless pathways. These three pathways are thought to act by setting up a gradient of a signalling molecule (or molecules) often referred to as the 'second signal'. Thus far, no candidate for a second signal has been identified. RESULTS: The four-jointed locus encodes a type II transmembrane protein that is expressed in a dorsoventral gradient in the developing eye disc. We have analysed the function and regulation of four-jointed during eye patterning. Loss-of-function clones or ectopic expression of four-jointed resulted in strong non-autonomous defects in ommatidial polarity on the dorsoventral axis. Ectopic expression experiments indicated that localised four-jointed expression was required at the time during development when ommatidial polarity was being determined. In contrast, complete removal of four-jointed function resulted in only a mild ommatidial polarity defect. Finally, we found that four-jointed expression was regulated by the Notch, JAK/STAT and Wingless pathways, consistent with it mediating their effects on ommatidial polarity. CONCLUSIONS: The clonal phenotypes, time of requirement and regulation of four-jointed are consistent with it acting in ommatidial polarity determination as a second signal downstream of Notch, JAK/STAT and Wingless. Interestingly, it appears to act redundantly with unknown factors in this process, providing an explanation for the previous failure to identify a second signal.

Polarity determination in the Drosophila eye: a novel role for unpaired and JAK/STAT signaling.

The JAK/STAT signaling pathway is required for many processes including cytokine signaling, hematopoiesis, gliagenesis, and Drosophila segmentation. In this report we present evidence demonstrating that the JAK/STAT pathway is also central to the establishment of planar polarity during Drosophila eye development. We show that a localized source of the pathway ligand, Unpaired, is present at the midline of the developing eye, which is capable of activating the JAK/STAT pathway over long distances. A gradient of JAK/STAT activity across the DV axis of the eye regulates ommatidial polarity via an unidentified second signal. Additionally, localized Unpaired influences the position of the equator via repression of mirror.

six-banded, a novel Drosophila gene, is expressed in 6 segmental stripes during embryonic development and in the eye imaginal disc.

We have characterised a Drosophila P-element enhancer detector insertion F125, which is expressed in the embryonic head and CNS as well as in various third instar imaginal discs. In an attempt to identify the gene with the equivalent expression pattern, we have characterised an adjacent gene. It encodes two novel conceptual proteins: Type I (1182 amino acids) and Type II, representing a shorter form of 774 amino acids truncated at both termini relative to Type I that is generated by alternative splicing. Based on its embryonic expression pattern, the gene was called six-banded (sba). Both splice forms are expressed in a unique embryonic pattern: initially as 6, then 12 stripes during early stages of embryonic development. Subsequently, expression is found in the developing trachae and during larval development is restricted to the eye imaginal disc where both transcripts are present immediately anterior to and behind the morphogenetic furrow. While sba expression in the eye antennal disc is mirrored by the expression of the adjacent F125 P-element, other patterns reported by this enhancer detector are not mimicked by the sba gene suggesting that the expression of the P-element represents a 'composite' of the effects of nearby enhancers.

Drosophila TFIIA-S is up-regulated and required during Ras-mediated photoreceptor determination.

Photoreceptor induction in the developing Drosophila eye is triggered by the activation of the Ras pathway. Subsequently, the Ras-mediated activation of site-specific transcription factors leads to the expression of putative "effector" genes. The coactivator function of the basal transcription factor TFIIA has been shown previously to enhance the trans-activation potential of site-specific transcription factors in vitro. Here, we show that the expression of the small subunit of TFIIA (dTFIIA-S) is specifically up-regulated in a transient manner during Ras-mediated photoreceptor induction. Furthermore, although null mutations in dTFIIA-S are cell lethal, a hypomorphic dTFIIA-S allele demonstrates an increased requirement for this factor during photoreceptor development. In addition, the cone cell to R7 photoreceptor transformation caused by ectopic activation of the Ras pathway during eye development is suppressed by the removal of one functional copy of the dTFIIA-S locus revealing the sensitivity of this process to reductions in dTFIIA-S activity. These results are the first in vivo evidence for the coactivator function in transcriptional enhancement proposed for TFIIA.

Drosophila TFIIA directs cooperative DNA binding with TBP and mediates transcriptional activation.

Drosophila transcription factor IIA (TFIIA) is composed of three subunits (30, 20, and 14 kD) that function during initiation of transcription. We reported previously the characterization of cDNAs that encode a precursor (dTFIIA-L) of the Drosophila TFIIA 30- and 20-kD subunits. In the absence of the smallest subunit, dTFIIA-S (14 kD), the unprocessed large subunit failed to exhibit any detectable promoter binding or transcriptional activity. Here, we report the molecular cloning and expression of dTFIIA-S, which has allowed the assembly of holo-dTFIIA (dTFIIA-L/S). Subunit interaction studies indicate that dTFIIA-S binds to an amino-terminal domain of dTFIIA-L, which likely corresponds to the endogenous 30-kD processed species. In addition, both dTFIIA-S and the carboxy-terminal domain of dTFIIA-L, which corresponds to the 20-kD species, independently interact weakly with the TATA-binding protein (TBP). In contrast, the holo-dTFIIA (L/S) binds TBP with high affinity. The dTFIIA-L/S complex also binds cooperatively with TBP to TATA box DNA sequences, generating an extended DNase footprint pattern. The reconstituted holo-dTFIIA is able to stimulate basal transcription of several core promoter templates. Interestingly, dTFIIA-L/S is also able to significantly enhance transcriptional activation by upstream transcription factors including Sp1, VP16, and NTF-1. These results suggest that dTFIIA is a multifunctional transcription factor capable of influencing DNA binding as well as interactions with the basal machinery, thereby enhancing activator-dependent transcription.

Comparative anatomy of serotonin-like immunoreactive neurons in isopods: putative homologues in several species.

It is now commonly accepted that the arthropod nervous system has evolved only once, and so homologies between crustacean and insect nervous systems can be meaningfully sought. To do this, we have examined the distribution of serotonin (5-hydroxytryptamine)-like immunoreactive neurons in the central nervous system (CNS) of four common British isopods. Two species of terrestrial woodlouse, Oniscus asellus and Armadillidium vulgare, the littoral sea slater, Ligia oceanica, and the aquatic water hoglouse, Asellus meridianus, all possess approximately 40 pairs of serotonin-like immunoreactive neurons, distributed throughout the CNS in a very similar pattern. Interspecific homology is clearly suggested. Serotonin-like immunoreactive neurons in the first (T1) and fourth (T4) thoracic ganglia are particularly prominent in each of the four species studied. Whole-mount immunohistochemistry shows that the pair of T1 neurons have large dorsolateral cell bodies and prominent neurites that project medially and then anteriorly, whereas the pair of T4 neurons have ventrolateral cell bodies and neurites that bifurcate to form a thin axon projecting anteriorly to terminate in T3 and a thick medial axon that projects posteriorly into the abdominal neuromeres of the terminal ganglion. Intracellular cobalt staining of these neurons reveals more of their arborizations: the T1 neurons send three processes anteriorly, which arborize in the brain and exist from the CNS via peripheral nerves, whereas the T4 neurons contribute considerably to the extensive pattern of serotonin-like immunoreactive fibres in T3-T6 ganglia. The overall pattern of serotonin-like immunoreactive neurons in the isopods is similar to that in decapod crustacea, and a number of putative homologies can be assigned. It is more difficult to homologize the isopod serotonin-like immunoreactive neurons with those in the insect CNS, but some stained brain and thoracic neurons share common cell body positions and axon trajectories in isopods, decapods, and insects and may therefore be homologous.