Invasion and metastases of cancer cells and the development of resistance to anticancer therapies are the main causes of morbidity and mortality from cancer. For more than two decades, these two important but not clearly related aspects in the biology of cancer have been extensively studied. Specifically, P-glycoprotein and CD44 have been characterized and are known to be determinants of multidrug resistance (MDR) and metastases. Despite this body of knowledge, few reports have linked the two phenotypes and only recently have there been reasons to suspect a direct connection. In this report, we show that a novel physical and genetic interaction between CD44s and P-glycoprotein is in part responsible for the correlation between MDR and invasive potential in cancer cells. P-glycoprotein-specific substrates that interfere with its function reduced in vitro invasion, migration, and the physical colocalization of CD44s and P-glycoprotein. CD44 expression in sensitive cells promoted the expression of P-glycoprotein and the MDR phenotype. RNA interference of MDR1 inhibited the rate of cell migration. These data indicate that there is a close interaction between CD44 and P-glycoprotein that results in the concurrent expression and modulation of two malignant phenotypes, invasion and MDR.

Background: CD44, a multifunctional receptor, undergoes cleavage to produce an intracytoplasmic domain (CD44-ICD) that translocates into the nucleus. Results: CD44-ICD binds to a novel DNA consensus sequence and activates many genes. Conclusion:We finally explain the multifunctionality of CD44 and reveal new genes affected by CD44. Significance: Our findings will accelerate the understanding of how CD44-ICD regulates a multitude of cell functions.

Here we demonstrate that a ubiquitin E3-ligase, FBXO21, targets the multidrug resistance transporter, ABCB1, also known as P-glycoprotein (P-gp), for proteasomal degradation. We also show that the Ser291-phosphorylated form of the multifunctional protein and stem cell marker, CD44, inhibits FBXO21-directed degradation of P-gp. Thus, CD44 increases P-gp mediated drug resistance and represents a potential therapeutic target in P-gp-positive cells.

Chronic inflammation is implicated in the pathophysiology of ovarian cancer. Tumor necrosis factor-A (TNF-A), a major inflammatory cytokine, is abundant in the ovarian cancer microenvironment. TNF-A modulates the expression of CD44 in normal T lymphocytes and CD44 is implicated in ovarian carcinogenesis and metastases. However, little is known about the role of TNF-A in CD44 expression of cancer cells. Recent clinical work using TNF-A inhibitors for the treatment of ovarian cancer makes the study of TNF-A interactions with CD44 crucial to determining treatment a success or a failure. We studied the effect of TNF-A on ovarian cancer cells viability, CD44 expression, and in vitro migration/invasion. Our results revealed that TNF-A differentially modulates the expression of CD44 in TNF-A-resistant ovarian cancer cells, affecting their in vitro migration, invasion, and binding to hyaluronic acid. TNF-A up-regulation of CD44 expression was dependent on the activation of c-Jun NH 2 -terminal kinase (JNK) and this activation was accompanied by an increase in their invasive phenotype. On the contrary, if TNF-A failed to induce JNK phosphorylation, the end result was down-regulation of both CD44 expression and the invasive phenotype. These results were confirmed by the use of JNK inhibitors and a TNF receptor competitive inhibitor.

CD44, a major hyaluronic acid (HA) receptor, is involved in cell migration, metastasis and tumor progression. While in normal ovarian epithelium CD44 is not expressed, ovarian carcinoma cells express multiple CD44 isoforms as the tumor progresses and eventually CD44 expression is abrogated in advanced ovarian cancer metastatic sites. We as well as others have observed that the levels of CD44 mRNA transcript not always correspond to the CD44 protein expression levels. This observation suggests that CD44 is post-transcriptionally regulated. To test this hypothesis we first analyzed the CD44 3’ untranslated region (3’ UTR) sequence and found numerous AU-rich elements (ARE) in this region. Some of these sequences are known HuR binding site consensus sequences. HuR is an RNA binding protein that is known to stabilize transcripts. HuR is expressed in the nucleus and is transported to the cytoplasm where it functions as an mRNA stabilizer. We performed mRNA half-life experiments that showed a two-fold reduction in the stability of CD44 transcript in siHuR transfected ovarian cancer cells. Consistent with this result, treatment of these cells with inhibitors of DNA methylation and histone deacetylation (i.e., 5-azacytidine and Trichostatin A, respectively) known to diminish the presence of HuR in the cytoplasm, also decreased the stability of CD44 mRNA. Western blot analysis showed the expected reduction in cytoplasmic HuR as well as down-regulation in CD44 protein expression. A direct interaction of HuR with the CD44 3’ UTR was detected by biotin pulldown assays. These results indicate that HuR posttranscriptionally stabilizes the expression of CD44 in the cytoplasm. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3078. doi:10.1158/1538-7445.AM2011-3078

Strains of the opportunistic fungal pathogen Candida albicans vary in the presence or absence of a self-splicing group I intron ribozyme (Ca.LSU) in the 25S rRNA gene on chromosome R. Strains of C. albicans typically either lack or contain this ribozyme. However, some strains have both intron-containing and intronless rRNA genes (rDNA). Pulsed-field gel electrophoresis analysis of undigested and restricted DNA showed at least six different karyotypes among eight independent colonies of such a heteroallelic strain. In each case, the variation was in chromosome R, and was due to changes in the number of rDNA units. In strains with only one type of rDNA, chromosome R also varied considerably. Polymerase chain reaction amplification spanning the rDNA unit demonstrated that intron-containing rDNA units are tandemly arrayed, and are immediately adjacent to intronless units in the same cluster. Both types of units were present in the rDNA clusters of both R chromosomes. Possible explanations of these results are loss of Ca.LSU group I intron through purifying selection and/or a relaxation of the commonly accepted concerted evolution of the rDNA units.