Inflammation leads to loss of smooth muscle cells but fails to induce invasiveness in a prostate tumor model

Inflammation has a causal role in many cancers. In prostate cancers, epidemiological data suggest a link between prostatitis and subsequent cancer development, but a proof for this concept in a tumor model has been lacking. A constitutively active version of the IkappaB kinase 2 (IKK2), the molecule activated by a plethora of inflammatory stimuli, was expressed specifically in the prostate epithelium. Signaling of the IKK2/NF-kappaB axis was insufficient for transformation of prostate tissue. However, while PTEN+/- epithelia exhibited intraepithelial neoplasias only recognizable by nuclear alterations, additional IKK2 activation led to an increase in tumor size and formation of cribriform structures and to a fiber increase in the fibroblastic stroma. This phenotype was coupled with inflammation in the prostate gland characterized by infiltration of granulocytes and macrophages. Molecular characterization of the tissues showed a specific loss of smooth muscle markers as well as expression of chemokines attracting immune cells. Isolation of epithelial and stromal cells showed differential chemokine expression by these cells. Correlation studies showed the inflammatory phenotype coupled to loss of smooth muscle in infiltrated glands, but maintenance of the phenotype in glands where inflammation had decreased. Despite the loss of the smooth muscle barrier, tumors were not invasive in a stable genetic background. Data mining revealed that smooth muscle markers are downregulated in human prostate cancers and literature data show that loss of these markers in primary tumors is associated with subsequent metastasis. Our data show that loss of smooth muscle and invasiveness of the tumor are not coupled. Thus, inflammation during early steps of tumorigenesis can lead to increased tumor size and a potential change in the subsequent metastatic potential, but the tumor requires an additional transformation to become a carcinoma.

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Birbach A, Eisenbarth D, Kozakowski N, Ladenhauf E, Schmidt-Supprian M, Schmid JA