Purpose: This study seeks to define immunologic and inflammatory variables associated with persistent post-treatment fatigue in breast cancer survivors. Experimental Design: Leukocyte subsets, plasma inflammatory markers, and ex vivo proinflammatory cytokine production were assessed in 50 fatigued and nonfatigued breast cancer survivors recruited z2 years after successful primary therapy. Multivariate statistical analyses were used to define a composite immunologic biomarker of fatigue risk. Results: Fatigued breast cancer survivors were distinguished from nonfatigued survivors by increased ex vivo monocyte production of interleukin (IL)-6 and tumor necrosis factor-a following lipopolysaccharide stimulation, elevated plasma IL-1ra and soluble IL-6 receptor (sIL-6R/CD126), decreased monocyte cell-surface IL-6R, and decreased frequencies of activated T lymphocytes and myeloid dendritic cells in peripheral blood (all P < 0.05). An inverse correlation between sIL-6R and cell-surface IL-6R was consistent with inflammation-mediated shedding of IL-6R, and in vitro studies confirmed that proinflammatory cytokines induced such shedding. Multivariate linear discriminant function analysis identified two immunologic markers, the ratio of sIL-6R to monocyte-associated IL-6R and decreased circulating CD69 + T lymphocytes, as highly diagnostic of fatigue (P = 0.0005), with cross-validation estimates indicating 87% classification accuracy (sensitivity = 0.83; specificity = 0.83). Conclusion: These results extend links between fatigue and inflammatory markers to show a functional alteration in proinflammatory cytokine response to lipopolysaccharide and define a prognostic biomarker of behavioral fatigue.

Converging evidence from basic and clinical studies suggests a role for proinflammatory cytokines in cancer-related fatigue, although the etiology of elevated inflammatory processes is unclear. We examined single nucleotide polymorphisms (SNPs) in the promoters of cytokine genes as genetic risk factors for cytokine-related fatigue in 33 fatigued and 14 non-fatigued breast cancer survivors, focusing on promoter sequence polymorphisms in IL1B and IL6 associated with differential expression of proinflammatory cytokines. Predictors of fatigue included presence of at least one cytosine at IL1B −511 (95%CI = 0.91–16.6, p = .007) and homozyosity for either variant of the IL6 −174 genotype (G/G or C/C; 95%CI = 1.12–17.9, p = .027). Associations between fatigue status and IL1B genotype remained significant after covariate adjustment for demographic, biobehavioral and treatment-related factors. These findings provide preliminary evidence that polymorphisms in IL1B may serve as a potential risk factor for persistent fatigue in the aftermath of cancer.

Loss of the CDK inhibitor p27KIP1 is widely linked with poor prognosis in human cancer. In Wnt10b-expressing mammary tumors, levels of p27 KIP1 were extremely low; conversely, Wnt10b-null mammary cells expressed high levels of this protein, suggesting Wnt-dependent regulation of p27 KIP1 . Interestingly we found that Wnt-induced turnover of p27 KIP1 was independent from classical SCF SKP2 -mediated degradation in both mouse and human cells. Instead, turnover required Cullin 4A and Cullin 4B, components of an alternative E3 ubiquitin ligase induced in response to active Wnt signaling. We found that CUL4A was a novel Wnt target gene in both mouse and human cells and that CUL4A physically interacted with p27 KIP1 in Wnt-responding cells. We further demonstrated that both Cul4A and Cul4B were required for Wnt-induced p27 KIP1 degradation and S-phase progression. CUL4A and CUL4B are therefore components of a conserved Wnt-induced proteasome targeting (WIPT) complex that regulates p27 KIP1 levels and cell cycle progression in mammalian cells.[Keywords: Basal-like breast cancer; reprogramming; Wnt-induced proteasome targeting (WIPT); mammary progenitor cells; mammary stem cell (MSC); Cdkn1b] Supplemental material is available at http://www.genesdev.org.

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