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Role of Bruton's tyrosine kinase (BTK) in growth and metastasis of INA6 myeloma cells.

Bam R, Venkateshaiah SU, Khan S, Ling W, Randal SS, Li X, Zhang Q, van Rhee F, Barlogie B, Epstein J, Yaccoby S - Blood Cancer J (2014)

Bottom Line: Bruton's tyrosine kinase (BTK) and the chemokine receptor CXCR4 are linked in various hematologic malignancies.BTK knockdown had reduced adhesion to stroma and migration of myeloma cells toward stromal cell-derived factor-1.BTK knockdown myeloma cells had altered the expression of genes associated with adhesion and proliferation and increased mammalian target of rapamycin signaling.

View Article: PubMed Central - PubMed

Affiliation: Myeloma Institute for Research and Therapy, University of Arkansas for Medical Sciences, Little Rock, AR, USA.

ABSTRACT
Bruton's tyrosine kinase (BTK) and the chemokine receptor CXCR4 are linked in various hematologic malignancies. The aim of the study was to understand the role of BTK in myeloma cell growth and metastasis using the stably BTK knockdown luciferase-expressing INA6 myeloma line. BTK knockdown had reduced adhesion to stroma and migration of myeloma cells toward stromal cell-derived factor-1. BTK knockdown had no effect on short-term in vitro growth of myeloma cells, although clonogenicity was inhibited and myeloma cell growth was promoted in coculture with osteoclasts. In severe combined immunodeficient-rab mice with contralaterally implanted pieces of bones, BTK knockdown in myeloma cells promoted their proliferation and growth in the primary bone but suppressed metastasis to the contralateral bone. BTK knockdown myeloma cells had altered the expression of genes associated with adhesion and proliferation and increased mammalian target of rapamycin signaling. In 176 paired clinical samples, BTK and CXCR4 expression was lower in myeloma cells purified from a focal lesion than from a random site. BTK expression in random-site samples was correlated with proportions of myeloma cells expressing cell surface CXCR4. Our findings highlight intratumoral heterogeneity of myeloma cells in the bone marrow microenvironment and suggest that BTK is involved in determining proliferative, quiescent or metastatic phenotypes of myeloma cells.

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Expression of CXCR4 and BTK is linked, and both genes are underexpressed in MM cells from focal lesions compared with random-site aspirates from the same patients. (a) Expression of CXCR4 and BTK was analyzed from cells of paired samples of focal lesions and random BM. Distributions of the differences for each pairwise comparison of each gene (CXCR4, P<7.58 × 10−13; BTK, P<1.58 × 10−7) are presented as box-and-whisker plots. Lower and upper edges of the boxes correspond to the first and third quartiles, respectively. The thicker bars in the middle represent the median, and the whiskers extend to the minimum and maximum values. (b) Plasma cells from random BM aspirates of patients with MM were analyzed for expression of BTK; samples were stratified according to the proportion of cells (⩽25% or >25%) with CXCR4 on their surfaces. (c) A model of intratumoral heterogeneity in myelomatous bone. Expression of BTK and CXCR4 in MM cells growing in interstitial BM is variable and is affected by interactions with matrix proteins and stromal cells. Prolonged persistence of MM cells in focal lesions results in mixed populations. BTK and CXCR4 expression impacts adherence and proliferative and metastatic behavior of these cells. BTK is essential for homing of MM cells from the circulation to the bone.
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fig6: Expression of CXCR4 and BTK is linked, and both genes are underexpressed in MM cells from focal lesions compared with random-site aspirates from the same patients. (a) Expression of CXCR4 and BTK was analyzed from cells of paired samples of focal lesions and random BM. Distributions of the differences for each pairwise comparison of each gene (CXCR4, P<7.58 × 10−13; BTK, P<1.58 × 10−7) are presented as box-and-whisker plots. Lower and upper edges of the boxes correspond to the first and third quartiles, respectively. The thicker bars in the middle represent the median, and the whiskers extend to the minimum and maximum values. (b) Plasma cells from random BM aspirates of patients with MM were analyzed for expression of BTK; samples were stratified according to the proportion of cells (⩽25% or >25%) with CXCR4 on their surfaces. (c) A model of intratumoral heterogeneity in myelomatous bone. Expression of BTK and CXCR4 in MM cells growing in interstitial BM is variable and is affected by interactions with matrix proteins and stromal cells. Prolonged persistence of MM cells in focal lesions results in mixed populations. BTK and CXCR4 expression impacts adherence and proliferative and metastatic behavior of these cells. BTK is essential for homing of MM cells from the circulation to the bone.

Mentions: We previously demonstrated the association between BTK expression and cell surface levels of CXCR4 in primary MM cells and that BTK expression is more profound in CXCR4+ than in CXCR4– MM cells sorted from the same patient sample.16 To further examine the intraclonal heterogeneity of MM cells with regard to these two factors, we analyzed the expression of BTK and CXCR4 in CD138-selected MM cells obtained from 176 paired samples—random-site BM aspirates and computed tomography-guided fine-needle aspirates of focal lesions defined by magnetic resonance imaging from the same patients. Expression of BTK (P<1 × 10−7) and CXCR4 (P<7 × 10−13) was significantly lower in samples from focal lesions than in those from random BM sites (Figure 6a). Furthermore, in samples from random-site BM aspirates that contained lower proportions (<25%) of MM cells with cell surface CXCR4, BTK expression was significantly lower than in samples with higher proportions (>25%) of MM cells with cell surface CXCR4 (Figure 6b). Thus, the differential expression of BTK and CXCR4 in focal lesions and interstitial marrow reflects intraclonal heterogeneity and points to the potential roles of distinct microenvironmental sites in regulating expression of these factors in MM cells.


Role of Bruton's tyrosine kinase (BTK) in growth and metastasis of INA6 myeloma cells.

Bam R, Venkateshaiah SU, Khan S, Ling W, Randal SS, Li X, Zhang Q, van Rhee F, Barlogie B, Epstein J, Yaccoby S - Blood Cancer J (2014)

Expression of CXCR4 and BTK is linked, and both genes are underexpressed in MM cells from focal lesions compared with random-site aspirates from the same patients. (a) Expression of CXCR4 and BTK was analyzed from cells of paired samples of focal lesions and random BM. Distributions of the differences for each pairwise comparison of each gene (CXCR4, P<7.58 × 10−13; BTK, P<1.58 × 10−7) are presented as box-and-whisker plots. Lower and upper edges of the boxes correspond to the first and third quartiles, respectively. The thicker bars in the middle represent the median, and the whiskers extend to the minimum and maximum values. (b) Plasma cells from random BM aspirates of patients with MM were analyzed for expression of BTK; samples were stratified according to the proportion of cells (⩽25% or >25%) with CXCR4 on their surfaces. (c) A model of intratumoral heterogeneity in myelomatous bone. Expression of BTK and CXCR4 in MM cells growing in interstitial BM is variable and is affected by interactions with matrix proteins and stromal cells. Prolonged persistence of MM cells in focal lesions results in mixed populations. BTK and CXCR4 expression impacts adherence and proliferative and metastatic behavior of these cells. BTK is essential for homing of MM cells from the circulation to the bone.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4219470&req=5

fig6: Expression of CXCR4 and BTK is linked, and both genes are underexpressed in MM cells from focal lesions compared with random-site aspirates from the same patients. (a) Expression of CXCR4 and BTK was analyzed from cells of paired samples of focal lesions and random BM. Distributions of the differences for each pairwise comparison of each gene (CXCR4, P<7.58 × 10−13; BTK, P<1.58 × 10−7) are presented as box-and-whisker plots. Lower and upper edges of the boxes correspond to the first and third quartiles, respectively. The thicker bars in the middle represent the median, and the whiskers extend to the minimum and maximum values. (b) Plasma cells from random BM aspirates of patients with MM were analyzed for expression of BTK; samples were stratified according to the proportion of cells (⩽25% or >25%) with CXCR4 on their surfaces. (c) A model of intratumoral heterogeneity in myelomatous bone. Expression of BTK and CXCR4 in MM cells growing in interstitial BM is variable and is affected by interactions with matrix proteins and stromal cells. Prolonged persistence of MM cells in focal lesions results in mixed populations. BTK and CXCR4 expression impacts adherence and proliferative and metastatic behavior of these cells. BTK is essential for homing of MM cells from the circulation to the bone.
Mentions: We previously demonstrated the association between BTK expression and cell surface levels of CXCR4 in primary MM cells and that BTK expression is more profound in CXCR4+ than in CXCR4– MM cells sorted from the same patient sample.16 To further examine the intraclonal heterogeneity of MM cells with regard to these two factors, we analyzed the expression of BTK and CXCR4 in CD138-selected MM cells obtained from 176 paired samples—random-site BM aspirates and computed tomography-guided fine-needle aspirates of focal lesions defined by magnetic resonance imaging from the same patients. Expression of BTK (P<1 × 10−7) and CXCR4 (P<7 × 10−13) was significantly lower in samples from focal lesions than in those from random BM sites (Figure 6a). Furthermore, in samples from random-site BM aspirates that contained lower proportions (<25%) of MM cells with cell surface CXCR4, BTK expression was significantly lower than in samples with higher proportions (>25%) of MM cells with cell surface CXCR4 (Figure 6b). Thus, the differential expression of BTK and CXCR4 in focal lesions and interstitial marrow reflects intraclonal heterogeneity and points to the potential roles of distinct microenvironmental sites in regulating expression of these factors in MM cells.

Bottom Line: Bruton's tyrosine kinase (BTK) and the chemokine receptor CXCR4 are linked in various hematologic malignancies.BTK knockdown had reduced adhesion to stroma and migration of myeloma cells toward stromal cell-derived factor-1.BTK knockdown myeloma cells had altered the expression of genes associated with adhesion and proliferation and increased mammalian target of rapamycin signaling.

View Article: PubMed Central - PubMed

Affiliation: Myeloma Institute for Research and Therapy, University of Arkansas for Medical Sciences, Little Rock, AR, USA.

ABSTRACT
Bruton's tyrosine kinase (BTK) and the chemokine receptor CXCR4 are linked in various hematologic malignancies. The aim of the study was to understand the role of BTK in myeloma cell growth and metastasis using the stably BTK knockdown luciferase-expressing INA6 myeloma line. BTK knockdown had reduced adhesion to stroma and migration of myeloma cells toward stromal cell-derived factor-1. BTK knockdown had no effect on short-term in vitro growth of myeloma cells, although clonogenicity was inhibited and myeloma cell growth was promoted in coculture with osteoclasts. In severe combined immunodeficient-rab mice with contralaterally implanted pieces of bones, BTK knockdown in myeloma cells promoted their proliferation and growth in the primary bone but suppressed metastasis to the contralateral bone. BTK knockdown myeloma cells had altered the expression of genes associated with adhesion and proliferation and increased mammalian target of rapamycin signaling. In 176 paired clinical samples, BTK and CXCR4 expression was lower in myeloma cells purified from a focal lesion than from a random site. BTK expression in random-site samples was correlated with proportions of myeloma cells expressing cell surface CXCR4. Our findings highlight intratumoral heterogeneity of myeloma cells in the bone marrow microenvironment and suggest that BTK is involved in determining proliferative, quiescent or metastatic phenotypes of myeloma cells.

Show MeSH
Related in: MedlinePlus