Ann M. Gifford

Cloning of the p50 DNA binding subunit of NF-κB : homology to rel and dorsal

The DNA binding subunit of the transcription factor NF-kappa B, p50, has been cloned. p50 appears to be synthesized as a larger protein that is then processed to its functional size. Sequence analysis reveals remarkable homology for over 300 amino acids at the amino-terminal end to the oncogene v-rel, its cellular homolog c-rel, and the Drosophila maternal effect gene dorsal. This establishes NF-kappa B as a member of the rel family of proteins, all of which display nuclear-cytosolic translocation. Protein sequence from the p65 polypeptide has established that it is not encoded in the same mRNA as p50. However, p65 appears homologous to c-rel, suggesting that c-rel may form heterodimers with p50 and rel may include a homodimerization motif.

Essential Roles for the Abl and Arg Tyrosine Kinases in Neurulation

The Abl and Arg tyrosine kinases play fundamental roles in the development and function of the central nervous system. Arg is most abundant in adult mouse brain, especially in synapse-rich regions. arg(-/-) mice develop normally but exhibit multiple behavioral abnormalities, suggesting that arg(-/-) brains suffer from defects in neuronal function. Embryos deficient in both Abl and Arg suffer from defects in neurulation and die before 11 days postcoitum (dpc). Although they divide normally, abl(-/-)arg(-/-) neuroepithelial cells display gross alterations in their actin cytoskeleton. We find that Abl and Arg colocalize with each other and with actin microfilaments at the apical surface of the developing neuroepithelium. Thus, Abl and Arg play essential roles in neurulation and can regulate the structure of the actin cytoskeleton.

Systemic endocrine instigation of indolent tumor growth requires osteopontin.

The effects of primary tumors on the host systemic environment and resulting contributions of the host to tumor growth are poorly understood. Here, we find that human breast carcinomas instigate the growth of otherwise-indolent tumor cells, micrometastases, and human tumor surgical specimens located at distant anatomical sites. This systemic instigation is accompanied by incorporation of bone-marrow cells (BMCs) into the stroma of the distant, once-indolent tumors. We find that BMCs of hosts bearing instigating tumors are functionally activated prior to their mobilization; hence, when coinjected with indolent cells, these activated BMCs mimic the systemic effects imparted by instigating tumors. Secretion of osteopontin by instigating tumors is necessary for BMC activation and the subsequent outgrowth of the distant otherwise-indolent tumors. These results reveal that outgrowth of indolent tumors can be governed on a systemic level by endocrine factors released by certain instigating tumors, and hold important experimental and therapeutic implications.

Human tumors instigate granulin-expressing hematopoietic cells that promote malignancy by activating stromal fibroblasts in mice

Systemic instigation is a process by which endocrine signals sent from certain tumors (instigators) stimulate BM cells (BMCs), which are mobilized into the circulation and subsequently foster the growth of otherwise indolent carcinoma cells (responders) residing at distant anatomical sites. The identity of the BMCs and their specific contribution or contributions to responder tumor growth have been elusive. Here, we have demonstrated that Sca1+ cKit- hematopoietic BMCs of mouse hosts bearing instigating tumors promote the growth of responding tumors that form with a myofibroblast-rich, desmoplastic stroma. Such stroma is almost always observed in malignant human adenocarcinomas and is an indicator of poor prognosis. We then identified granulin (GRN) as the most upregulated gene in instigating Sca1+ cKit- BMCs relative to counterpart control cells. The GRN+ BMCs that were recruited to the responding tumors induced resident tissue fibroblasts to express genes that promoted malignant tumor progression; indeed, treatment with recombinant GRN alone was sufficient to promote desmoplastic responding tumor growth. Further, analysis of tumor tissues from a cohort of breast cancer patients revealed that high GRN expression correlated with the most aggressive triple-negative, basal-like tumor subtype and reduced patient survival. Our data suggest that GRN and the unique hematopoietic BMCs that produce it might serve as novel therapeutic targets.

Lethal effect of the abelson murine leukemia virus transforming gene product

Infection of NIH/3T3 and Balb/c/3T3 fibroblastic cell lines by Abelson virus results in stable transformation in most cases. We have observed that certain rodent cell lines, including some Balb/c/3T3 sublines, do not maintain stable transformation following infection. Within three to four weeks of infection of these cell lines a large fraction of the cells is not recoverable upon serial passage and appear to be killed. The residual population of cells displays a flat, nontransformed phenotype. Concomitant with this reversion is the loss of the integrated provirus and loss of expression of the Abelson virus transforming protein. This loss of the integrated provirus is specific to transformation-competent viral strains. The effect of Abelson virus on these cells appears to be, in part, due to a lethal effect of the transforming protein on the cells. We have selectively isolated mutants of Abelson virus that stably transform these rodent cell lines without expressing a lethal effect. Analysis of the nucleic acid and protein structure of these mutant virus strains showed that the transforming proteins are shorter, having lost expression of the carboxy-terminal one third of the protein. We suspect that the carboxy-terminal portion of the wild-type Abelson protein may modulate the in vivo expression of the protein kinase activity and that this may cause the transforming protein to have a deleterious effect on certain cell lines.

Purified bovine NF-kappa B recognizes regulatory sequences in multiple genes expressed during activation of T- and B-lymphocytes.

To characterize the NF-kappa B binding factor in molecular terms and to facilitate the cloning of its gene, we have purified this protein from bovine spleen tissue. We have found it is a 42,000-dalton protein that exists in solution as a dimer. We were able to use the purified protein to show that the same polypeptide is able to recognize sites important for activation of genes in either B- or T-lymphocytes. Moreover, we were able to define a consensus sequence which allows ascertainment of a wider variety of sequences that are capable of interacting with this protein. The implication of the same protein in gene regulation in two different lineages of lymphoid cells reveals an unexpected unity in the mechanism of gene expression during B- and T-lymphocyte activation. This also suggests that other regulatory events must participate with NF-kappa B activation in determining B- or T-cell-specific expression.

IL-1β inflammatory response driven by primary breast cancer prevents metastasis-initiating cell colonization

Lack of insight into mechanisms governing breast cancer metastasis has precluded the development of curative therapies. Metastasis-initiating cancer cells (MICs) are uniquely equipped to establish metastases, causing recurrence and therapeutic resistance. Using various metastasis models, we discovered that certain primary tumours elicit a systemic inflammatory response involving interleukin-1β (IL-1β)-expressing innate immune cells that infiltrate distant MIC microenvironments. At the metastatic site, IL-1β maintains MICs in a ZEB1-positive differentiation state, preventing MICs from generating highly proliferative E-cadherin-positive progeny. Thus, when the inherent plasticity of MICs is impeded, overt metastases cannot be established. Ablation of the pro-inflammatory response or inhibition of the IL-1 receptor relieves the differentiation block and results in metastatic colonization. Among patients with lymph node-positive breast cancer, high primary tumour IL-1β expression is associated with better overall survival and distant metastasis-free survival. Our data reveal complex interactions that occur between primary tumours and disseminated MICs that could be exploited to improve patient survival.Castaño et al. show that primary breast tumours drive an IL-1β -mediated inflammatory response that inhibits cellular plasticity and metastatic colonization of metastasis-initiating cells.

Abstract PR13: Understanding the systemic interactions between primary tumors and disseminated tumor initiating cells

The causes for breast cancer recurrence in the form of metastatic disease and the reasons why less than 1% of disseminated tumor cells form metastases are unknown. A number of studies have demonstrated that the aggressive cancer cell population capable of driving metastasis feature properties of the epithelial-mesenchymal transition (EMT) and tumor initiation (TI). We previously reported novel mechanisms by which systemic and microenvironmental factors enrich tumors for EMT and TI genes and demonstrated that recurrence rates are not strictly due to tumor cell intrinsic properties (Castano et al., Cancer Discovery 2013). Using a preclinical model of breast cancer during the early phases of metastatic disease, when patients harbor disseminated tumor initiating cells (TICs) in the periphery at the time of their primary diagnosis (McAllister SS et al., Cell 2008), we recently made a surprising, and seemingly contrasting discovery. Specifically, we found that certain primary tumors can inhibit progression of disseminated TICs into overt tumors, maintaining them in the TI state and slowing their proliferation and differentiation to form tumor tissue mass. We established that the primary tumor induce mobilization of IL1beta-expressing monocytes that are recruited to sites where TICs reside. At those sites, signaling via the IL1 receptor maintains the EMT/TI state of the disseminated cells, thus promoting disease indolence. Importantly, surgical removal of the primary tumor enables TICs at the secondary sites to exit the EMT/TI state and to produce robustly growing tumors. Confirming our xenograft results, we established that stromal expression of IL1β in patient tumors is associated with poor outcome. Collectively, these data highlight the profound impact a primary tumor can exert on metastasizing cells - in this case, by altering the systemic environment to the detriment of secondary tumor growth. Moreover, our data highlight a central role for IL1β in modulating tumor cell plasticity and suggest it may provide a novel avenue for targeting recurrent disease. Citation Format: Zafira Castano, Christine L. Chaffer, Asaf Spiegel, Ayush Pant, Andrea L. Richardson, Ferenc Reinhardt, Timothy Marsh, Susanne Janssen, Ann M. Gifford, Robert A. Weinberg, Sandra S. McAllister. Understanding the systemic interactions between primary tumors and disseminated tumor initiating cells. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr PR13.

Abstract C75: Granulin‐expressing bone marrow cells promote the outgrowth of indolent tumors

We previously demonstrated that certain vigorously growing xenografted human carcinomas (“instigators”) stimulate the growth of otherwise‐indolent carcinoma cells and metastases (“responders”) implanted at distant anatomical sites — a process we termed “systemic instigation” (S. McAllister, et al.; Cell, 2008). We showed that systemic instigation is largely the result of activation of bone marrow cells (BMCs) that subsequently contribute to the stroma of the responding tumors; however, the identity of the activated BMCs and their contribution to outgrowth of the once‐indolent cells was unknown. Here, we demonstrate that Sca1+/cKit− BMCs of hosts bearing instigating tumors are activated prior to their mobilization into the circulation and are very potent in their ability to promote outgrowth of the responding tumors. Strikingly, responding tumors, which result from either the presence of a contralateral instigating tumor or the admixture of Sca1+/cKit− BMCs harvested from instigator‐bearing mice, form with a desmoplastic stroma. Stromal desmoplasia, the accumulation of a myofibroblast‐rich reactive connective tissue, is almost always observed in malignant human adenocarcinomas. The Sca1+/cKit− BMCs do not directly give rise to stromal myofibroblasts; instead, we found that factors secreted by these BMCs induce fibroblasts to express alpha‐smooth muscle actin (ACTA2), a myofibroblast marker. Gene expression profiling of the Sca1+/cKit− BMCs from instigator‐ and non‐instigator‐bearing mice identified granulin, a pluripotent secreted growth factor, as the most highly upregulated gene in the activated BMCs. We found: i) that granulin is indeed expressed by bone marrow‐derived cells that are recruited into the responding tumor stroma; ii) that treatment of human mammary fibroblasts with granulin induces ACTA2 expression; iii) that granulin treatment is sufficient to enhance responding tumor growth in vivo . Mining of existing microarray datasets revealed that high granulin expression is correlated with the expression of ACTA2 in human breast cancers and is associated with shorter disease‐free survival of breast cancer patients. Our results indicate that the formation of desmoplastic stroma, a condition that is associated with invasive carcinomas, can be instigated systemically by certain tumors via activation of granulin‐expressing Sca1+/cKit− in the bone marrow. Citation Information: Cancer Res 2009;69(23 Suppl):C75.