AMERICAN EXPRESS CO., $59.44, New York symbol AXP, rose 2% this week on speculation that WELLS FARGO &CO., $50.05, New York symbol WFC, will soon launch a takeover offer. Berkshire Hathaway (New York symbol BKB.B), the holding company controlled by billionaire investors Warren Buffett, owns 15.6% of American Express and 9.8% of Wells Fargo. An acquisition would enhance Wells Fargo’s credit card business and give it access to Amex’s high-quality clientele. In addition, the bank’s large depositor base provides a lower-cost way of funding credit card loans. Combining the two businesses would also allow Wells Fargo to eliminate overlapping operations. It’s unclear if banking regulators would approve a merger. Even if a deal fails to materialize, we still like Amex’s long-term prospects. The company plans to cut $1 billion from its annual costs in the next two years. That will help offset the loss of business from Costco. That retailer recently dropped Amex as the only credit card it accepts at its U.S….