Theresa P. Pretlow

Epigenetic inactivation of SFRP genes allows constitutive WNT signaling in colorectal cancer

Aberrant WNT pathway signaling is an early progression event in 90% of colorectal cancers. It occurs through mutations mainly of APC and less often of CTNNB1 (encoding β-catenin) or AXIN2 (encoding axin-2, also known as conductin). These mutations allow ligand-independent WNT signaling that culminates in abnormal accumulation of free β-catenin in the nucleus. We previously identified frequent promoter hypermethylation and gene silencing of the genes encoding secreted frizzled-related proteins (SFRPs) in colorectal cancer. SFRPs possess a domain similar to one in the WNT-receptor frizzled proteins and can inhibit WNT receptor binding to downregulate pathway signaling during development. Here we show that restoration of SFRP function in colorectal cancer cells attenuates WNT signaling even in the presence of downstream mutations. We also show that the epigenetic loss of SFRP function occurs early in colorectal cancer progression and may thus provide constitutive WNT signaling that is required to complement downstream mutations in the evolution of colorectal cancer.

A new human prostate carcinoma cell line, 22Rv1

SummaryA cell line has been derived from a human prostatic carcinoma xenograft, CWR22R. This represents one of very few available cell lines representative of this disease. The cell line is derived from a xenograft that was serially propagated in mice after castration-induced regression and relapse of the parental, androgen-dependent CWR22 xenograft. Flow cytometric and cytogenetic analysis showed that this cell line represents one hyper DNA-diploid stem line with two clonal, evolved cytogenetic sublines. The basic karyotype is close to that of the grandparent xenograft, CWR22, and is relatively simple with 50 chromosomes. In nude mice, the line forms tumors with morphology similar to that of the xenografts, and like the parental CWR22 and CWR22R xenografts, this cell line expresses prostate specific antigen. Growth is weakly stimulated by dihydroxytestosterone and lysates are immunoreactive with androgen receptor antibody by Western blot analysis. Growth is stimulated by epidermal growth factor but is not inhibited by transforming growth factor-β1.

SLC5A8, a sodium transporter, is a tumor suppressor gene silenced by methylation in human colon aberrant crypt foci and cancers

We identify a gene, SLC5A8, and show it is a candidate tumor suppressor gene whose silencing by aberrant methylation is a common and early event in human colon neoplasia. Aberrant DNA methylation has been implicated as a component of an epigenetic mechanism that silences genes in human cancers. Using restriction landmark genome scanning, we performed a global search to identify genes that would be aberrantly methylated at high frequency in human colon cancer. From among 1,231 genomic NotI sites assayed, site 3D41 was identified as methylated in 11 of 12 colon cancers profiled. Site 3D41 mapped to exon 1 of SLC5A8, a transcript that we assembled. In normal colon mucosa we found that SLC5A8 exon 1 is unmethylated and SLC5A8 transcript is expressed. In contrast, SLC5A8 exon 1 proved to be aberrantly methylated in 59% of primary colon cancers and 52% of colon cancer cell lines. SLC5A8 exon 1 methylated cells were uniformly silenced for SLC5A8 expression, but reactivated expression on treatment with a demethylating drug, 5-azacytidine. Transfection of SLC5A8 suppressed colony growth in each of three SLC5A8-deficient cell lines, but showed no suppressive effect in any of three SLC5A8-proficient cell lines. SLC5A8 exon 1 methylation is an early event, detectable in colon adenomas, and in even earlier microscopic colonic aberrant crypt foci. Structural homology and functional testing demonstrated that SLC5A8 is a member of the family of sodium solute symporters, which are now added as a class of candidate colon cancer suppressor genes.

15-Hydroxyprostaglandin dehydrogenase is an in vivo suppressor of colon tumorigenesis

15-Hydroxyprostaglandin dehydrogenase (15-PGDH) is a prostaglandin-degrading enzyme that is highly expressed in normal colon mucosa but is ubiquitously lost in human colon cancers. Herein, we demonstrate that 15-PGDH is active in vivo as a highly potent suppressor of colon neoplasia development and acts in the colon as a required physiologic antagonist of the prostaglandin-synthesizing activity of the cyclooxygenase 2 (COX-2) oncogene. We first show that 15-PGDH gene knockout induces a marked 7.6-fold increase in colon tumors arising in the Min (multiple intestinal neoplasia) mouse model. Furthermore, 15-PGDH gene knockout abrogates the normal resistance of C57BL/6J mice to colon tumor induction by the carcinogen azoxymethane (AOM), conferring susceptibility to AOM-induced adenomas and carcinomas in situ. Susceptibility to AOM-induced tumorigenesis is mediated by a marked induction of dysplasia, proliferation, and cyclin D1 expression throughout microscopic aberrant crypt foci arising in 15-PGDH null colons and is concomitant with a doubling of prostaglandin E2 in 15-PGDH null colonic mucosa. A parallel role for 15-PGDH loss in promoting the earliest steps of colon neoplasia in humans is supported by our finding of a universal loss of 15-PGDH expression in microscopic colon adenomas recovered from patients with familial adenomatous polyposis, including adenomas as small as a single crypt. These models thus delineate the in vivo significance of 15-PGDH-mediated negative regulation of the COX-2 pathway and moreover reveal the particular importance of 15-PGDH in opposing the neoplastic progression of colonic aberrant crypt foci.

Carcinoembryonic antigen in human colonic aberrant crypt foci

BACKGROUND/AIMS Aberrant crypt foci are putative preneoplastic lesions that, by definition, are identified microscopically in whole-mount preparations of colonic mucosa. Because the identification of hexosaminidase as a marker for rat aberrant crypt foci in histological sections facilitated their characterization, a similar marker for human foci in histological sections was sought. METHODS Human aberrant crypt foci were marked in whole-mount preparations, embedded in paraffin, and evaluated for their expression of carcinoembryonic antigen with two monoclonal antibodies. RESULTS Elevated expression of carcinoembryonic antigen was detected in 39 of 42 (93%) aberrant crypt foci from 15 patients. The expression of carcinoembryonic antigen assisted in the evaluation of longitudinal sections of foci, where dysplasia is more readily detected in these small lesions. The expression of carcinoembryonic antigen was related to the sizes of the foci (P = 0.0085, generalized Fishers Exact Test) but not to the presence or degree of dysplasia. CONCLUSIONS The overexpression of immunohistochemically demonstrable carcinoembryonic antigen is, to date, the only described alteration in most of these putative precursors of human colon cancer that differs from the expression in contiguous, normal crypts at the histological level and thus facilitates the identification of aberrant crypts in histological sections for further characterization.

Cytologic Characterization of Pulmonary Alveolar Macrophages by Enzyme Histochemistry in Plastic

Quantitative morphometric analyses of macrophages should facilitate a more precise definition of the role of macrophages in neoplastic diseases and inflammatory diseases of lymphoid and hemopoietic tissues. The usefulness of the available phenotypic markers is affected by the extent to which they are expressed by macrophages in tissue sections. For our study of phenotypic markers for macrophages in human tissue sections, we selected lung, since pulmonary alveolar macrophages are more readily identified morphologically in tissue sections than macrophages in most other tissues. In 1-2 micron sections of freshly fixed lung embedded in methacrylate, 89.7% of pulmonary alveolar macrophages had histochemically demonstrable acid phosphatase; 86.2%, nonspecific esterase with naphthol ASD chloroacetate as the substrate; 86.2%, nonspecific esterase with alpha-naphthyl butyrate as the substrate; 80.5%, peroxidase; and 75.8%, iron. With respect to their expression of markers, the observed heterogeneity among pulmonary alveolar macrophages is interesting; this heterogeneity may reflect the degree to which they have been activated, the different periods of time since they arrived in the lung, and differences in their local environments. Except for peroxidase, all examined markers were as well demonstrated when tissues were fixed after storage over liquid nitrogen as when fixation was carried out with fresh tissue. Acid phosphatase and nonspecific esterase with the chloroactetate substrate gave bright colors that would facilitate morphometric analyses. The storage of tissue over liquid nitrogen will be equally satisfactory for the characterization of macrophages with histochemical markers and monoclonal antibodies.

Increased expression of fatty acid synthase in human aberrant crypt foci: possible target for colorectal cancer prevention

Aberrant crypt foci (ACF), the earliest identified monoclonal lesions in the colon, provide insights into changes that promote and/or accompany the transformation of normal colonic epithelial cells to colorectal cancer. Fatty acid synthase (FAS), the primary enzyme involved in de novo lipogenesis from carbohydrates, is expressed at low levels in most normal human tissues but is elevated in several human neoplasms including colorectal adenomas and carcinomas. To determine if this pathway is altered even earlier in colorectal tumorigenesis, 35 human ACF from 21 patients were evaluated for the immunohistochemical expression of FAS. Sections of colon cancer served as positive controls, and normal colonic mucosa distant from cancer or ACF served as negative controls. FAS expression was increased in 30 (86%) ACF compared with that in adjacent normal colonic mucosa. The expression of FAS in ACF was not related to the degree of dysplasia or to the number of crypts in the ACF. The over expression of FAS in a high proportion of ACF suggests that this enzyme plays an important role very early in colorectal tumorigenesis and may be a target for chemoprevention.

β-Catenin expression and allelic loss at APC in sporadic colorectal carcinogenesis

Abstract β-catenin is involved in E-cadherin-mediated cell adhesion, intracellular signal transduction, and also interacts with adenomatous polyposis coli (APC) protein. We previously found that 31% of colorectal adenomas and 84% of carcinomas showed reduced membranous staining of β-catenin, while 46% of adenomas and 79% of carcinomas displayed β-catenin nuclear expression. Importantly, a reciprocal relationship between reduced membranous and increased nuclear β-catenin expression was demonstrated in the development from adenoma to carcinoma. To clarify whether this relates to an abnormality of the APC gene (APC), we have now studied allele loss in microdissected tissues from 74 adenomas and 21 carcinomas (sporadic cases, previously immunostained for β-catenin) by analysis of the microsatellites D5S346, D5S82 and D5S299. Fifty-five tumors (57.8%) showed allele loss at APC (no difference between adenomas and carcinomas). Thirty-one of these 55 (31/55, 56.4%) displayed both increased nuclear localization and reduced membranous staining of β-catenin, and thirteen tumors (13/55, 23.6%) manifested either nuclear expression without changes in membranous expression or reduced membranous staining without nuclear expression (9 and 4 cases, respectively), while 11 (11/55, 20.0%) preserved normal membranous expression. Adenomas and carcinomas showing both nuclear and reduced membranous expression of β-catenin, compared with those with normal membranous expression, tended to show allele loss (P<0.01). In addition, 24 (24/95, 25.6%) tumors showed a change in the pattern of β-catenin expression, but did not exhibit allele loss. These results suggest that although there may be a number of mechanisms responsible for changes in β-catenin expression in colorectal tumors, dysfunction of APC may be the major cause of this phenomenon.

Differential experimental micrometastasis to lung, liver, and bone with lacZ-tagged CWR22R prostate carcinoma cells.

LacZ-tagged human prostate carcinoma CWR22Rv1 cells metastasize spontaneously to lung, liver, and bone from subcutaneous primary tumors in athymic nude mice; these organs are ‘natural’ targets of metastasis for the human disease. To evaluate the mechanism(s) of metastasis to these organs, an experimental metastasis model was used by taking advantage of the ultrasensitive detection of lacZ. Within 1 h after tail vein injection, micrometastases were forming in lung, liver, bone, kidney, and brain with very different quantitative levels. The kinetics of loss of unstable micrometastases and retention of stable ones were also very different in these organs. After injecting suspensions of single cells, both whole-organ and serial-section staining for lacZ revealed considerable heterogeneity in cell number of individual lung micrometastases while micrometastases in liver contained only 1 or 2 cells. The size of individual bone micrometastases also suggested only 1 or 2 cells. Tumor cells could also be detected in the small blood vessels of the lung within minutes after injection. These studies indicate that lacZ-tagged CWR22Rv1 cells after tissue culturing contain subsets of cells capable of establishing transient micrometastases in lung, liver, and bone after direct injection into the animal’s circulation. Moreover, the quantitative and qualitative properties of the micrometastases in the three organs differ significantly, suggesting different mechanisms for stabilization and fates of micrometastases in these organs.

Sedimentation of Cells: An Overview and Discussion of Artifacts

Publisher Summary This chapter discusses sedimentation at unit gravity, elutriation, isokinetic sedimentation, and the separation of cells by velocity sedimentation in a reorienting gradient zonal rotor. The term velocity sedimentation refers to the kind of sedimentation that occurs before cells arrive at their respective buoyant densities. For most kinds of velocity sedimentation, it is desirable to use gradients with densities as remote as possible from the densities of the cells. For maximal resolution, these gradients should increase in the concentration of solute. There are four forms of velocity sedimentation that are broadly applicable to the separation of viable cells: sedimentation at unit gravity, sedimentation in an isokinetic gradient of Ficoll in tissue culture medium, elutriation or counter-streaming centrifugation, and centrifugation in a reorienting gradient zonal rotor. Sedimentation at unit gravity and isokinetic sedimentation offer the investigator two major advantages: (1) Cells can be separated under sterile conditions with a high degree of reliability and (2) the necessary equipment is either available in most laboratories or very inexpensive. Both techniques are best suited for work with relatively small numbers of cells. In contrast, elutriation and sedimentation in a reorienting zonal rotor require much more skill and care if they are to be used for work under sterile conditions. Isopycnic or buoyant density sedimentation refers to the sedimentation of cells in continuous gradients with sufficient force and for a sufficient period of time for them to arrive at the locations of their respective densities in the gradient.